Minerals

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Minerals

source http://ga.gov.au
            http://www.galleries.com/Silicates
            http://academic.brooklyn.cuny.edu/geology/grocha/mineral/cleavage.html
            http://butane.chem.uiuc.edu/pshapley/Environmental/L26/2.html
           http://www.tulane.edu/~sanelson/eens211/silicate_structures08.htm

kyanite

Mineral Identification Basics
Mineral Groups
Silicates
Sulphates
Sulphides
Table of common non-metallic minerals and their properties
Table of common metallic minerals and their properties
click here to open a large mineral identification flow chart in a new window...
List of common minerals and their images...
    see also E-Learning - Minerals...
    see also Petrology - Mineral Optics...


banded iron formation

Mineral Identification Basics

Colour

The colour of a mineral is a result of the mineral's light absorbing and light reflecting properties.  These may vary greatly in vitreous minerals with the presence of traces of impurities.  Colour is therefore not always an indication of identity in a vitreous specimen, although it is a more reliable indicator with opaque minerals.

colour

An excellent example of the above is quartz.  Six different varieties of quartz are each a different characteristic colour despite having identical chemical compositions (SiO2):
Rock Crystal - colourless
Amethyst - purple
Citrine - yellow, to orange-brown
Smokey Quartz - brown or grey
Rose Quartz - pink
Milky Quartz - white
It is also worth remembering that completely different minerals may be the same colour.


Streak

The streak of a mineral is the colour of it's powder when rubbed along an unglazed porcelain plate (streak-plate) and may be different from the colour of the mineral itself.

streak

Powder may also be produced by scratching the mineral with a knife.  The streak of any given mineral is consistent for that mineral despite any differences in colour.  The six different varieties of quartz above all have the same white streak.


Lustre

The mineral's appearance due to the amount and quality of light reflected from it's surfaces.  Depending on the quality of light a mineral reflects it may appear:
Adamantine - the lustre of diamond
Vitreous - the lustre of broken glass, e.g.. quartz
Subvitreous - as vitreous, less well developed
Resinous - the lustre of resin, e.g.. amber and opal
Pearly - the lustre of pearl
Silky - the lustre of silk in fibrous minerals such as satin spar gypsum
Metallic - the lustre of metal
Submetalic - as metallic, poorly displayed

metallic lustre

Depending on the quantity or intensity of light a mineral reflects it may appear:
Splendent
Shining
Dull


Transparency


Form

The form of a crystal is dependant upon the conditions under which it grew.  For example growth may have occurred outwards into a melt unhindered or it may have been restricted by the presence of other solid matter. 
The following terms are used to describe form:
Crystallized - the mineral occurs as well developed crystals
Crystalline - the mineral occurs as an aggregate of confused, imperfect crystals which hindered each other's formation during growth.  These minerals often have a granular, sparkling appearance due to light reflected from the small crystal faces.
Cryptocrystalline or Microcrystalline - crystals are very small and are hidden from the naked eye, but show under a microscope.
Glass - random arrangement of atoms; no crystal structure.  A substance which cooled so rapidly that crystals did not have time to form.  The result may be thought of as a stiff, brittle supercooled liquid.


Habit

The habit of a specimen (the shape of it's crystals) is greatly affected by the conditions under which the crystals grew.  It is quite common for a mineral to have many different habits. 
The terms used to describe a specimen's habit are split into two groups;
(1) the habit of crystals,
(2) the habit of crystal aggregates.

quartz crystal

1. Crystal Habits
Prismatic - crystal is elongated along one axis
Tabular - Broad, flat crystals
Acicular - needle-like crystals
Bladed - the shape of a knife blade
Fibrous - fine thread fibres as in asbestos and satin spar gypsum
Foliaceous - composed of thin separate leaves (lamellae) as in mica.
Lamellar - separable into individual plates or lamellae
Reticulate - cross-mesh pattern
Scaly - small plates
Individual crystals may be described by their shape i.e.. cubic, hexagonal elongated (prismatic),
lozenge, rhombohedral, octohedral, etc.

2. Crystal Aggregate Habits
Amygdales - are spherical aggregates infilling vesicles in 'amygdaloidal' rocks.
Massive columnar - such as in stalactites and stalagmites aggregates.
Nodular - such as flint nodules in chalk
Granular or Saccharoidal - grains, may range from coarse to fine.  Saccharoidal means 'sugar-like'.
Mammilated - similar to reniform (below), but more spherical outer surfaces.  e.g.. malachite.
Reniform - 'kidney-shaped' rounded outer surface.  e.g. haematite / hematite
A mineral with no crystal or aggregate shape is a glass.

Crystal Systems

- many minerals form crystals as they cool. There are six systems of crystals based on their geometry.
For each system listed below there are some examples of minerals belonging to that system.
"click on any link to see an image of the mineral"
triclinic crystal
Triclinic Minerals include: albite, amblygonite, anapaite, andesine, anorthite, anothoclase, astrophyllite, axinite, babingtonite, baumhauerite, bustamite, bytownite, ceruleite, chabazite-(Ca), chalcanthite, chalcosiderite, chloritoid (triclinic), collinsite, copiapite, cornubite, cuprosklodowskite, cylindrite, diadochite, emmonsite, fairfieldite, ferroaxinite, fiedlerite, fluckite, frankeite, gageite-1tc, gordonite, halloysite, hydrodresserite, inesite, jamesite, kermesite, kyanite, labradorite, lengenbachite, ludlockite, manganaxinite, manganbabingtonite, metakottingite, microcline, miserite, montebrasite, nambulite, nealite, oligoclase, paradamite, paravauxite, pectolite, picropharmacolite, planerite, pyrophyllite, pyroxmangite, rhodonite, sapphirine, serandite, serendibite, serpentine, strunzite, symplesite, tarbuttite, tinzenite, turquoise, ulexite, ussingite, vauxite, weloganite, wollastonite, amesite, donnayite-(Y), epistilbite, epistolite, hilgardite, kaolinite, leucophanite, magnesio-axinite, murmanite, nacaphite, nefedovite, tundrite and tyretskite.

tetragonal crystal
Tetragonal Minerals include: apophyllite, autunite, meta-autunite, torbernite, meta-torbernite, xenotime, carletonite, plattnerite, zircon, hausmannite, pyrolusite, thorite, anatase, vesuvianite, rutile and cassiterite
 
orthorombic crystal
Orthorhombic Minerals include: barite group minerals as well as sulfur, staurolite, olivine, andalusite, members of the aragonite group minerals, marcasite, topaz, brookite, enstatite, anthrophyllite, sillimanite, zoisite, adamite, danburite, cordierite, wavellite

monoclinic crystal
Monoclinic Minerals include: acanthite, actinolite, aegirine, allanite, annabergite, arfvedsonite, arsenopyrite, augite, aurichalcite, azurite, bannisterite, beryllonite, biotite, borax, boulangerite, brazilianite, brochantite, butlerite, calaverite, carnotite, catapleiite, caledonite, celsian, chalcocite, charoite, chondrodite, chrysotile serpentine, clinochlore, clinoclase, clinoptilolite, colemanite, cookeite, cornwallite, creedite, crocoite, cryolite, cryptomelane, cummingtonite, datolite, diopside, dufrenite, edenite, epidote, erythrite, esperite, euclase, fluorrichterite, gadolinite, gaylussite, gibbsite, glauberite, glauconite, graftonite, gypsum, harmotome, hedenbergite, hessite, heulandite, hodgkinsonite, hornblende, howlite, hubnerite, hydroboracite, hydromagnesite, hydrozincite, illite, jadeite, jamesonite, jordanite, kernite, kidwellite, kieserite, kinoite, kottingite, kovdorskite, ktenasite, lamprophyllite, lanarkite, langbanite, laumontite, lazulite, leadhillite, legrandite, leucosphenite, linarite, liroconite, ludlamite, malachite, manganite, melanterite, monazite, montmorillonite, muscovite, olivenite, orpiment, orthoclase, palygorskite, papagoite, pargasite, phillipsite, phlogopite, polybasite, polylithionite, pseudomalachite, psilomelane, pyrrhotite, realgar, richterite, riebeckite, romanechite, rosasite, roselite, sanidine, sauconite, semseyite, sklodowskite, sphene, spodumene, staurolite, stilbite, stringhamite, sussexite, sylvanite, synchysite, tainiolite, talc, tenorite, thomsenolite, titanite, tremolite, trona, vermiculite, veszelyite, vivianite, volborthite, whewellite, whiteite, wohlerite, wolframite, xonotlite, zinnwaldite, zippeite and zirconolite-2M

isometric crystal
Isometric Minerals include: fluorite, galena, diamond, copper, iron, lead, platinum, silver, gold, halite, bromargyrite, chlorargyrite, moschellandsbergite, murdochite, osbornite, periclase, pollucite, villiaumite, pyrochlore, thorianite, the garnet group, uraninite, most members of the spinel group, pentlandite, sylvite, analcime

hexagonal crystal
Hexagonal Minerals include: calcite group as well as corundum, hematite, bismuth, antimony, sturmanite, brucite, arsenic, soda niter, chabazite, millerite, quartz, tellurium berlinite, cinnabar, tourmaline group, pyrargyrite, jarosite, natrojarosite, alunite, proustite,dolomite group, ankerite, ilmenite, dioptase, willemite, phenakite,

Amorphous Minerals

-show no crystal structure
Amorphous Minerals include: amber, limonite, obsidian, opal, petroleum, shungite, tektite

"click on any link to see an image of the mineral"


Cleavage

Cleavage is the tendency of a mineral to split in certain preferred directions when struck.  These directions are parallel to sheets of atoms in the mineral's atomic lattice.

cleavage

Calcite has good cleavage in three directions parallel to its rhombohedral habit and is therefore said to have rhombohedral cleavage.
Fluorite has a cubic habit, but it has four cleavage directions which cut across it's corners to leave an octahedral core.  Therefore fluorite has octahedral cleavage.

cleavage based on crystal form


Fracture

The fracture of a mineral is how it breaks other than along cleavage planes.  The fracture may be described as: Conchoidal - a 'shell-like', convex or concave fracture displaying curved fracture or undulation rings concentric to the point of impact and lines or fractures radial from the point of impact, as in quartz, flint and obsidian.

conchoidal fracture

Even - a flat fracture, as in chert
Uneven - a rough fracture surface.  This is the most common type of fracture.
Hackly - jagged sharp ridges, such as in native copper.


Hardness

The hardness of a mineral is measured on Moh's scale.  The scale lists hardness values from 1 to 10.  The numbers may be treated as relative values except for diamond; i.e. fluorite(4) is twice the hardness of gypsum(2).  Diamond(10) is about ten times the hardness of corundum(9).  Each value has a corresponding mineral of thathardness.  Therefore the hardness of a mineral can be tested relative to the minerals on Moh's scale by scratching them with those minerals and other household items of known hardness.
Moh's scale of hardness
moh's scale of hardness

Density


The relative density of a mineral is its mass divided by it's volume.  The specific gravity of a mineral is it's mass divided by the mass of an equal volume of water.  In the field it is adequate to simply 'heft' a specimen to determine whether it is of low, high or moderate weight compared to it's size.
Silicates and other non-metallic minerals are the least dense with SGs of 2.5 to 3.5
Metallic minerals are denser with SGs from 5 upwards (typically 5 to 8).  Gold has an SG of 19 to 20.

Vitreous minerals are usually 'light' and metallic usually dense, but be aware that there are always exceptions to the rule.

Table Showing Specific Gravities of Minerals

Low SG Medium SG High SG Very High SG
  (all vitreous) (all metallic) (metal ores)
       
gypsum muscovite barite cassiterite
halite (rock salt) biotite malachite galena
graphite calcite sphalerite  
  fluorite chalcopyrite  
  hornblende haematite/ hematite  
  augite magnetite  
  orthoclase pyrite  
  plagioclase    
  olivine    
  quartz    


Magnetism

Magnetite and pyrrhotite are magnetic and will be affected by a bar magnet.  Other iron minerals are magnetic to a lesser extent, but cannot be tested by an ordinary magnet in the field.  Large iron-bearing masses may affect the orientation of compass needles.  A petrology lecturer described how he once stopped for lunch on a large magnetite-bearing outcrop and then set off in completely the wrong direction and wasted the rest of the day.Is this mineral magnetic (try using a compass), or is it attracted by a magnet? This property is characteristic of Magnetite.

Effervescence

This one is most popular with the kiddies as well as the new geology student (welcome). When some minerals are exposed to acids, they begin to fizz. This is a great method you can use to identify the mineral calcite (see TASTE). You can also use this one to detect the presence of calcite in rocks.


Birefringence


birefringence
This is also known as double refraction.
Birefringent minerals split the light into two different rays which gives the illusion of double vision in this Iceland Spar Calcite.

Fluoresence

fluorescence
Some minerals display what is called the phenomenon of photoluminescence. This basically means that they "glow" when exposed to UV light (black light). The above mineral (opal) is demonstrating fluoresence. Also, the mineral Fluorite is often strongly fluorescent. Do you see a connection? Fluorite --> Fluoresence

Taste

This will quickly identify the mineral halite (salt). If you are new to this process you must use this one with caution, as you never know what the unknown may be. Often, you may need to resort to this method (until you more fully understand other identifying traits) to differentiate halite from calcite. If you do taste the sample (especially in a class environment) you should realize that it has been handled by and probably tasted by hundreds of others.

Odour

Pyrite, sphalerite and chalcopyrite give a sulphurous 'rotten egg' smell
when struck or rubbed on a streak plate.  haematite and limonite may give off
an 'earthy' smell (the smell of damp earth) when breathed upon.

Sparkle

Pyrite sparkes when struck with a geological hammer.  I have also
experienced this effect with haematite.

Feel

Crystalline minerals will feel rough.  Talc and serpentine often feel
unctuous (greasy) or soapy.  Graphite and satin spar gypsum may
feel smooth, unctous or soapy.  Graphite is a good conductor of
heat and will therefor feel cold.

Conductivity

Graphite is also a good conductor of electricity (it is used a brushes on
electric motors), but this property would not be tested in the field.Graphite is a good example

Acid Reaction

Carbonate minerals react with dilute hydrochloric acid: Calcite effervesces strongly in dil. HCl
Malachite also reacts strongly
Dolomite reacts weakly in warm dil. HCl or if scratched
to produce a little powder prior to applying the acid
Siderite reacts weakly

Tenacity

Tenacity describes how the mineral behaves when subjected to deformation: Brittle - The minerals breaks or crumbles easily, such as fluorite.

Mineral Groups

Minerals are divided into the following groups:

Carbonates

carbonate structure

Carbonate Minerals are based on the salt calcium carbonate.
Calcium Carbonate ionic bonds between the calcium +2 cations and the carbonate -2 anions. There are strong, covalent bonds within the CO32- group.
The carbonate minerals have a structure that is similar to the cubic close packed structure found in halite (NaCl) where the Na cations are replaced by divalent cations (Ca, Mg, Fe, Mn, Sr, Ba, Pb, etc.) and the Cl anions are replaced by CO32- polyatomic trigonal planar ions. Think of the ions as being located on two face-centered cubic lattices that interpenetrate one another.
 
Minerals in the carbonate group differ do not have true cubic close packed symmetry because anions and the cations differ significantly in size. They are distorted from this type of crystal form.
Limestone, a sedimentary rock, becomes marble from the heat and pressure of metamorphic events. Calcite is even a major component in the igneous rock called carbonatite.
Dolomite, CaMg(CO3)2, is a common sedimentary rock-forming mineral that can be found in massive beds several hundred feet thick. They are found all over the world and are quite common in sedimentary rock sequences. All dolomite rock was initially deposited as calcite/aragonite rich limestone, but during a process call diagenesis the calcite and/or aragonite is altered to dolomite.

All carbonates have some water solubility and dissolve readily in acidic water. They dissolve in acidic water and can recrystallize from the water. Metal ions are frequently trapped in the lattice spaces during crystallization.
This leads to carbonates with a variety of colors and crystal forms.
 
Carbonic acid-rich water forms caves in limestone. When the water table is high, carbonic acid-rich water dissolves the limestone (calcite). Later when the water table drops, a void filled with air is formed. Smaller amounts of water rich in Ca2+ and HCO3- may continue to flow through the void. These waters decrease the CO2 partial pressure in the atmosphere of the cave and aqueous CO2 is released into the gas phase. This increases the pH and drives the precipitation of calcite and formation of stalagmites, stalactites and other cave features. Salts containing the carbonate anion decompose with loss of carbon dioxide. This is an endothermic reaction and produces metal oxide materials. The carbonates are more stable, in general, with larger cations.

decomposition of a carbonate

Halides


NaCl "salt"

Halides are formed by combining a metal with one of the five halogen elements, chlorine, bromine, fluorine, iodine, and astatine.
Many of these compounds will dissolve in water and are often associated with evaporating seas.
Halite (NaCl) or rock salt is the most common.
Other halides minerals include: Fluorite CaF2 or calcium fluoride and Sylvite KCl or potassium chloride 

Native Elements


Australian gold nugget

Minerals found naturally and composed of just one element  - examples gold, silver, copper

Oxides


corundum crystal

The oxide mineral class includes those minerals in which the oxide anion (O2−) is bonded to one or more metal ions.
It includes: gemstones such as Corundum (Aluminum Oxide), Chrysoberyl (Beryllium Aluminum Oxide), Spinel (Magnesium Aluminum Oxide)
metallic ores such as Hematite (Iron Oxide), Ilmenite (Iron Titanium Oxide), Magnetite (Iron Oxide), Chromite (Iron Chromium Oxide)
The hydroxide bearing minerals are typically included in the oxide class
Hydroxide minerals include: Limonite (Hydrated Iron Oxide Hydroxide), Manganite (Manganese Oxide Hydroxide), Gibbsite (Aluminum Hydroxide)

Silicates

Silicates are the largest, the most interesting, and the most complicated class of minerals by far. Approximately 30% of all minerals are silicates and some geologists estimate that 90% of the Earth's crust is made up of silicates. With oxygen and silicon the two most abundant elements in the earth's crust, the abundance of silicates is no real surprise. The basic chemical unit of silicates is the (SiO4) tetrahedron shaped anionic group with a negative four charge (-4). The central silicon ion has a charge of positive four while each oxygen has a charge of negative two (-2) and thus each silicon-oxygen bond is equal to one half (1/2) the total bond energy of oxygen. This condition leaves the oxygens with the option of bonding to another silicon ion and therefore linking one (SiO4) tetrahedron to another and another, etc..
The complicated structures that these silicate tetrahedrons form is truly amazing. They can form as single units, double units, chains, sheets, rings and framework structures. The different ways that the silicate tetrahedrons combine is what makes the Silicate Class the largest, the most interesting and the most complicated class of minerals.

The Nesosilicate Subclass (single tetrahedrons)  neosilicate


The simplest of all the silicate subclasses, this subclass includes all silicates where the (SiO) tetrahedrons are unbonded to other tetrahedrons. In this respect they are similar to other mineral classes such as the sulfates and phosphates. These other classes also have tetrahedral basic ionic units (PO4 & SO4) and thus there are several groups and minerals within them that are similar to the members of the nesosilicates. Nesosilicates, which are sometimes referred to as orthosilicates, have a structure that produces stronger bonds and a closer packing of ions and therefore a higher density, index of refraction and hardness than chemically similar silicates in other subclasses. Consequently, There are more gemstones in the nesosilicates than in any other silicate subclass. Below are the more common members of the nesosilicates. See the nesosilicates' page for a more complete list.

Sorosilicate Subclass (double tetrahedrons)  sorosilicate

Sorosilicates have two silicate tetrahedrons that are linked by one oxygen ion and thus the basic chemical unit is the anion group (Si2O7) with a negative six charge (-6). This structure forms an unusual hourglass-like shape and it may be due to this oddball structure that this subclass is the smallest of the silicate subclasses. It includes minerals that may also contain normal silicate tetrahedrons as well as the double tetrahedrons. The more complex members of this group, such as Epidote, contain chains of aluminum oxide tetrahedrons being held together by the individual silicate tetrahedrons and double tetrahedrons. Most members of this group are rare, but epidote is widespread in many metamorphic environments. Below are the more common members of the sorosilicates. See the sorosilicates' page for a more complete list.

Inosilicate Subclass (single and double chains)   inosilicae single chain   inosilicate double chain

This subclass contains two distinct groups: the single chain and double chain silicates. In the single chain group the tetrahedrons share two oxygens with two other tetrahedrons and form a seemingly endless chain. The ratio of silicon to oxygen is thus 1:3. The tetrahedrons alternate to the left and then to the right along the line formed by the linked oxygens although more complex chains seem to spiral. In cross section the chain forms a trapezium and this shape produces the angles between the crystal faces and cleavage directions.
In the double chain group, two single chains lie side by side so that all the right sided tetrahedrons of the left chain are linked by an oxygen to the left sided tetrahedrons of the right chain. The extra shared oxygen for every four silicons reduces the ratio of silicons to oxygen to 4:11. The double chain looks like a chain of six sided rings that might remind someone of a child's clover chain. The cross section is similar in the double chains to that of the single chains except the trapezium is longer in the double chains. This difference produces a difference in angles. The cleavage of the two groups results between chains and does not break the chains thus producing prismatic cleavage. In the single chained silicates the two directions of cleavage are at nearly right angles (close to 90 degrees) forming nearly square cross sections. In the double chain silicates the cleavage angle is close to 120 and 60 degrees forming rhombic cross sections making a convenient way to distinguish double chain silicates from single chain silicates. Below are the more common members of the inosilicates. See the Inosilicates' page for a more complete list.
Single Chain Inosilicates:
The Double Chain Inosilicates:

Cyclosilicate Subclass (rings)   cyclosilicate

These silicates form chains such as in the inosilicates except that the chains link back around on themselves to form rings. The silicon to oxygen ratio is generally the same as the inosilicates, (1:3). The rings can be made of the minimum three tetrahedrons forming triangular rings (such as in benitoite). Four tetrahedrons can form a rough square shape (such as in axinite). Six tetrahedons form hexagonal shapes (such as in beryl, cordierite and the tourmalines). There are even eight membered rings and more complicated ring structures. The symmetry of the rings usually translates directly to the symmetry of these minerals; at least in the less complex cyclosilicates. Benitoite's ring is a triangle and the symmetry is trigonal or three-fold. Beryl's rings form hexagons and its symmetry is hexagonal or six-fold. The Tourmalines' six membered rings have alternating tetrahedrons pointing up then down producing a trigonal as opposed to an hexagonal symmetry. Axinite's almost total lack of symmetry is due to the complex arrangement of its square rings, triangle shaped borate anions (BO3) and the position of OH groups. Cordierite is pseudo-hexagonal and is analogous to beryl's structure except that aluminums substitute for the silicons in two of the six tetrahedrons. There are several gemstone minerals represented in this group, a testament to the general high hardness, luster and durability. Below are the more common members of the cyclosilicates. See the Cyclosilicates' page for a more complete list.

Phyllosilicate Subclass (sheets)   phyllosilicate

In this subclass, rings of tetrahedrons are linked by shared oxygens to other rings in a two dimensional plane that produces a sheet-like structure. The silicon to oxygen ratio is generally 1:2.5 (or 2:5) because only one oxygen is exclusively bonded to the silicon and the other three are half shared (1.5) to other silicons. The symmetry of the members of this group is controlled chiefly by the symmetry of the rings but is usually altered to a lower symmetry by other ions and other layers. The typical crystal habit of this subclass is therefore flat, platy, book-like and display good basal cleavage. Typically, the sheets are then connected to each other by layers of cations. These cation layers are weakly bonded and often have water molecules and other neutral atoms or molecules trapped between the sheets. This explains why this subclass produces very soft minerals such as talc, which is used in talcum powder. Some members of this subclass have the sheets rolled into tubes that produce fibers as in asbestos serpentine.
Below are the more common members of the phyllosilicates. See the Phyllosilicates' page for a more complete list.

The Tectosilicate Subclass (frameworks)   tectosilicate

This subclass is often called the "Framework Silicates" because its structure is composed of interconnected tetrahedrons going outward in all directions forming an intricate framework analogous to the framework of a large building. In this subclass all the oxygens are shared with other tetrahedrons giving a silicon to oxygen ratio of 1:2. In the near pure state of only silicon and oxygen the mineral is quartz (SiO2). But the tectosilicates are not that simple. It turns out that the aluminum ion can easily substitute for the silicon ion in the tetrahedrons up to 50%. In other subclasses this substitution occurs to a more limited extent but in the tectosilicates it is a major basis of the varying structures. While the tetrahedron is nearly the same with an aluminum at its center, the charge is now a negative five (-5) instead of the normal negative four (-4). Since the charge in a crystal must be balanced, additional cations are needed in the structure and this is the main reason for the great variations within this subclass. Below are the more common members of the tectosilicate subclass. See the tectosilicates' page for a more complete list.

Sulphates


sulphate ion

Sulphate minerals include the sulfate ion (SO42−) within their structure. The sulfate minerals occur commonly in primary evaporite depositional environments, as gangue minerals in hydrothermal veins and as secondary minerals in the oxidizing zone of sulfide mineral deposits. Common examples include gypsum (CaSO4·2H2O) and anhydrite (CaSO4) in evaporitic sediments; barite (BaSO4), which is deposited from hydrothermal fluids; and anglesite (PbSO4), an alteration product of lead sulfide ores.

Sulphides


zinc sulphide
Sulphide minerals include the sulphide anion within their structure S-2
Common examples include the important metallic minerals: Sphalerite (Zinc Iron Sulfide), Galena (Lead Sulfide), Molybdenite (Molybdenum Sulfide), Pyrite (Iron Sulfide), Chalcopyrite (Copper Iron Sulfide)
The vast majority of sulfide minerals are components of hydrothermal sulfide ores. Some sulfides of Fe, Ni, Cu, and Pt are associated with processes of magma formation in ultrabasic rocks. Sulfide minerals may be of sedimentary origin, or they may be exogenous, having been deposited from surface solutions under the action of H2S—for example, in coal-bearing strata and in oxidation zones of sulfide deposits.



Non-metallic Minerals and their Properties

"click on a link to see an image of the mineral"
N.B. most (if not all) minerals with colour listed as 'colourless' may
be tinted almost any colour by the presence of trace impurities.
NAME
FORMULA 		HABIT LUSTRE
S.g. 		USUAL COLOUR/
STREAK 		HARDNESS
CLEAVAGE 		OTHER
PROPERTIES 		OCCURRENCE
USES
Calcite CaCO3
rhombohedral,
dog tooth and
nail head
crystals 		vitreous 2.7
colourless or white white
3 3 perfect, rhombohedral
effervesces vigorously
in dil. HCl.
double
refraction
of images
viewed
throught it		 as limestone,
 in veins, as stalactites, stalagmites lime fertilizer, cement,
flux in steel industry
Selenite gypsum CaSO42H2O
lozenge
crystals,
often
fishtail twins		 vitreous 2.3
colourless, white white
2 1 perfect, parallel to crystal faces

evaporites
and
free-growing
 in clays plaster-of
-paris, plasterboard
 ie. Gyproc
Alabaster
gypsum CaSO
42H2O
crystalline,
granular 		vitreous 2.3
colourless, white white
2 n/a

evaporites plaster-of
-paris, plasterboard
 ie. Gyproc
Satin spar
gypsum CaSO4
2H2O
fibrous vitreous 2.3
colourless, white white
2 n/a

evaporites plaster-of
-paris, plasterboard
 i.e.. Gyproc
Halite
(rock salt) NaCl
 
cubic
crystals,
with hollow
stepped faces		 vitreous 2.2
colourless, white white
2 - 2.5 3 good, cubic
tastes
 of salt,
 soluble
in water
(so clean
it in petrol)		 evaporite,
 playa
lake deposit food
 processing, washing
soda
Quartz SiO2
elongated
 hexagonal
prisms capped
by pyramids,
 or crystalline granular		 vitreous 2.65
colourless in rock crystal - see guide to properties for other varieties white
7 none
horizontal
striations
on crystal
faces,
conchoidal
fracture 		as sand and sandstone,
 in veins,
as geodes, constituent
 in many
igneous and metamorphic
rocks microchips,
gemstone.  concrete and  glass making
 (as sand)
Barite BaSO4
tabular
crystals,
reticulate
crystals,
or radiating
bladed
'cockscomb' structures in crystalline form		 vitreous 4.5
colourless, white white
2.5 - 3.5 3 good, 1 horizontal (basal), 2 vertical (at 90 degrees to basal)
heaviest
vitreous
mineral
at s.g.4.5		 vein mineral used in
paint
and paper,
 and
as a
drilling
mud in the oil industry
Biotite mica K2(Mg,Fe2+)
6-4(Fe3+
Al,Ti)0-
2[Si6-5Al2
-3O20]
OH,F)4
foliaceous,
platey,
pseudo-
hexagonal
crystals 		pearly 3.0
brown, black white
2.5 - 3 1 perfect basal

a common
 rock forming
 mineral in sedimentary, metamorphic
 and igneous
 rocks used for
furnace
windows
heat
resistant
formica
and as
glitter in
a wide
range of products.
Muscovite
mica K2Al4
[Si6Al2O20]
(OH,F)4
foliaceous,
platey,
pseudo-
hexagonal
crystals 		pearly 3.0
silvery-white (named after Moscow in 'White Russia' white
2 - 2.5 1 perfect basal

a common
rock forming
mineral in sedimentary, metamorphic
and igneous
rocks used for
furnace
windows
heat
resistant
formica
and as
glitter
in a wide
range of products.
Fluorite,
Blue John CaF2
cubic
crystals
or as
crystalline
 masses 		vitreous, sometimes a very slightly greasy or watery appearance 2.7
colourless, blue & yellow as blue john variety white
4 4 perfect octohedral:-  cleavage planes cut across corners of 6-sided cubic crystals to leave 8-sided octohedral cores.
blue john
is coloured
 by oil
impurities
 and is
only found
in situ
at Mam Tor
 in
Derbyshire,
UK 		vein mineral semi-
precious gemstone
as blue john (from French; bleu-blue jaune-yellow).  Also used
as flux
 in steel
smelting
Orthoclase
feldspar (complex
framework silicate)
prismatic,
tabular or rectangular
crystals 		vitreous to pearly about 2.6
colourless (may be cloudy), white, pink or pale red, other pale colours also white
6 (a moh's scale mineral) 2 cleavages at 90 degrees
sub-
transparant
 to
translucent orthoclase
 is
named
after it's 2 cleavages
at
right angles:
ortho=right
klastos
=breaks, 
common
rock forming
mineral in
igneous, metamorphic
and sedimentary rocks used in
vitreous chinaware
and as an abraisive in scouring powders.
Plagioclase
feldspar (complex
framework silicate)
prismatic,
tabular or rectangular
crystals 		vitreous to pearly about 2.7
white or grey to grey-blue or other pale colours white
6 - 6.5 2 cleavages at almost 90 degrees
sub-
transparant
 to
translucent plagioclase
 is named after its 2 cleavages
at almost
right
angles:
plagio=almost
klastos=breaks
common
rock forming
 mineral in
igneous, metamorphic
and sedimentary rocks used in
vitreous chinaware
and as an abraisive in scouring powders.
Oligoclase
feldspar (complex
framework silicate)
prismatic,
 tabular or rectangular
 crystals 		vitreous to pearly about 2.6
white or pale colours white
2 cleavages at almost 90 degrees 6 - 6.5
sub-
transparant
to
translucent oligoclase
is named
after it's cleavages
 at a few degrees
from a
right angle:
oligo=a few
klastos
=breaks
common
rock forming
mineral in
igneous, metamorphic
 and
sedimentary
 rocks used in
vitreous chinaware
and as an abraisive in scouring powders.
Olivine FeMgSiO4
tabular
crystals or
granular
crystalline
masses 		vitreous 2.5 - 3.5 (more often ~3.5)
green, may also be yellow or brown white
1 poor cleavage, cracks on what appears to be second cleavage plane; actually a sub-parallel fracture 6 - 7

occurs in
basic and
ultrabasic
igneous rock
, best
crystals
occur in olivine-peridotite gemstone
Garnet (a group of Fe,Ca,Al,Cr,
Mn & Mg,
silicate minerals)
rhombo-
dodecahedral, dodecahedral and tetra-
hexahedral crystals,
also as
angular fragments		 vitreous 3.6 - 4.3
deep red, crimson, purple, brown, black, olive, greens, pink, yellow white
no cleavage 7 - 7.5 (except gossular variety, which may be as low as 6.5)

a dense
mineral
formed in
high pressure
/temperature condition in metamorphic
rocks used as a gemstone
 and as an abraisive
(garnet
paper is
 a red
abraisive
paper
used on
wood).
Malachite Cu2[(OH)
2CO3]
crypto-
crystalline 		dull 4.0
emerald green, or other shades of green light green,
good 4.0

a weathering
product of
copper
deposits
Chrysocolla Cu4H4
[(OH)8Si4
O10]
crypto-
crystalline 		dull 2.0 - 2.3
blue-green pale green or blue-green
none 2 - 4

in oxidation
zones in
copper
ore deposits


Metallic Minerals and their Properties

"click link to see an image of the mineral"

NAME
FORMULA 		HABIT LUSTRE
S.g. 		USUAL COLOUR/
STREAK 		HARDNESS
CLEAVAGE 		OTHER
PROPERTIES 		OCCURRENCE
USES
Galena PbS
cubic crystals metallic 7.5
silver-grey grey-black
2.5 3; perfect cubic cleavage

vein mineral, often with calcite, fluorspar and barites cheif source of lead (Pb).
Haematite / Hematite Fe2O3
reniform aggregate habit earthy 5
Red-brown red-brown
5.5 to 6.5 2 poor cleavages
sub-conchoidal or uneven fracture often in limestones as a relacement minerals, also in metamorfphic deposites, ironstones and as both thin veins and cement in sandstones eg. the New Red Sandstone iron ore and used as a pigment in paint 'Red Ochre'
Pyrite FeS2
cubic crystals, or as pentagonal dodecahedral crystals.  Also as nodules with an internal structure of radiating needles, also as crystalline masses metallic 5.0
brass-yellow black
6 - 6.5 no cleavage
cubic crystals often have striated faces,
conchoidal fracture, 
sparks when struck with geological hammer 
pyrite = fire mineral.
smells sulphurous when rubbed on a streak plate		 occurs as free crystals or nodules in coal, clay and shales, also in veins formerly source of sulphur, used to make sulphuric acid (native sulphur now main source).
Sphalerite (aka zinc blende, black jack) ZnS
usually massive aggregates, also tetrahedral crystals resinous, sometimes brilliant or adamantine on fresh surfaces 4.0
brown or black pale yellow
3.5 - 4 perfect cleavage in 6 directions
smells sulphurous when rubbed on a streak plate vein mineral chief source of [non-corrosive] zinc, used for galvanisation of iron
Chalcopyrite CuFeS2
octohedral and tetrahedral crystals metallic 4.1 - 4.3
brass-yellow black or greenish-black
3.5 - 4.0 indistinct

ore mineral

List of common minerals and their images

'click on any name to see an image..."
anhydrite   apatite 1   2   arsenopyrite   asbestos   barite   calcite 1  2    cassiterite  chalcopyrite 1  2   chlorite   chromite  corundum   diamond   feldspar-albite   feldspar-microcline      feldspar-orthoclase 1  2  3  4      feldspar-plagioclase 1  2  3  fluorite1 2 galena 1  2   garnet   gold   graphite   gypsum 1  2  halite(salt)   hematite/haematite    hornblende 1  2   ilmenite   kyanite   limonite   magnetite 1  2     manganese ore   mica-biotite1  2   mica-muscovite1  2  3   mica-phlogopite   molybdenite   olivine   pyrite1  2   pyroxene1  2     pyrrhotite   quartz1  2  3  4  5  6  rutile  siderite   smaltite   sphalerite1  2   stibnite   talc1  2  3   topaz1  2   tourmaline   zircon