Minerals - ESO 3 Biology and Geology

What to Learn?

In this section: - Summary of contents covered by this page.

Organic matter vs inorganic matter. Geochemical elements.
Crystalline matter vs. amorphous matter. Crystals vs. glasses. Minerals vs. mineraloids.
Physical properties of the minerals: crystal structure, growth habit, density, hardness, tenacity, cleavage, lustre, colour, streak, others.
Classification of the minerals. Some important minerals and their physical properties.
Obtaining minerals. Beds and mines.
Uses of the minerals. Main metallic ores. Main gemstones.

Basic Information

Physical Properties of the Minerals

Colour	The colour of a mineral is one of its most obvious attributes and the easiest physical property to determine. Unfortunately, as it results from a minerals chemical composition and structure, the impurities and structural flaws that may be present can alter completely the colour with regards to the pure mineral. Hence minerals like fluorite and quartz may display a really wide range of colours. This makes colour not the most useful property in helping to characterize a particular mineral.
Streak	The streak refers to the colour of a mineral's powder, which is almost always the same, regardless the impurities and structural flaws of the mineral. Thus, it is much more reliable to characterize a mineral than the colour of the mineral itself. The streak is usually obtained by rubbing the mineral across a plate of unglazed porcelain. The streak and the mineral's typical colour may or may not be the same. Some examples of streaks of common minerals are pyrite (black), magnetite (black), halite (white).
Transparency / Diaphaneity	A transparent mineral (diamond) allows all light to cross through; a translucent mineral (quartz) allows part of the light to cross through; an opaque mineral (pyrite) does not allow the light to pass at all.
Lustre	It refers to the way in wich a mineral's surface reflects light. To some extent it is related to the transparency of a mineral; for instance, metallic minerals are always opaque and vitreous minerals are always translucent.
Cleavage	In some minerals, bonds between layers of atoms aligned in certain directions are weaker than bonds between different layers. In these cases, breakage occurs along flat surfaces parallel to those zones of weakness. In some minerals, a single direction of weakness exists, but as many as six may be present. Halite, which forms cubic crystals, presents 3 perfect cleavage directions.
Hardness	It depends on the strength of the chemical bonds and is measured by the ease or difficulty with which a mineral can be scratched. Diamond is the hardest mineral, because it can scratch all others. Talc is one of the softest; nearly every other mineral can scratch it. We measure a mineral's hardness by comparing it to the hardnesses of a standardized set of minerals first established by Friederich Mohs.
Tenacity	It is a mineral's physical reaction to stress such as crushing, bending, breaking, or tearing. For example, according to its tenacity, a mineral can be brittle (easy to powder with a hammer), sectil (easy to cut with a knife), malleable (easy to flatten with a hammer, as metallic minerals) or ductile (easy to stretch into a wire, as metallic minerals).
Growth habit	Refers to the shape a mineral develops when it is not constricted by lack of available space. For example, quartz forms six-sided prisms capped with pyramid-like faces; halite occur as cubes; and pyrite develop cubes or pentadodecahedrons (polyhedrons with 12 pentagonal faces).
Specific gravity	It's a comparison of the density of a mineral to that of water. For example, quartz has a specific gravity of 2.6 because it is 2.6 greater than that of water. You can also say that it has a density of 2.6 g/cm³
Magnetism	When a mineral can be attracted by a magnet or act themselves as magnets. The best example is magnetite.
Electrical conduction	Wether an electric current can easily pass through a mineral (such as in all metallic minerals and graphite) or not.
Feel	What you perceive when you touch a mineral. It can be rough, smooth, greasy (talc), cold (diamond)...
Taste	What you perceive when you lick a mineral. Halite, for instance, tastes salty.

Main Types of Mineral Lustre

Lustre	Opacity	Examples
Adamantine	Transparent	Diamond
Vitreous	Translucent	Quartz, Halite, Olivine
Wet	Translucent	Fluorite
Resinous	Translucent	Yellow and red sphalerite varieties
Waxy	Translucent	Talc
Greasy	Variable	Milky quartz
Silky	Variable	Fibrous gypsum
Pearly	Poorly translucent	Orthoclase, Mica aggregates
Dull metallic	Opaque	Cinnabar aggregates
Metallic	Opaque	Pyrite, Chalcopyrite, Magnetite
Earthy	Opaque	Kaolinite

Properties of Some Common Minerals

	Composition	Colour	Streak	Transparency	Lustre	Hardness	Growth habit
Quartz	SiO₂	Colourless, white, grey, yellow, violet...	White	Translucent	Vitreous	7	6-sided prisms
Olivine	Silicate	Olive green	White	Translucent	Vitreous	6.7	Granular
Biotite / Black mica	Silicate	Colourless / Black (aggr.)	Grey	Translucent	Vitreous / Pearly (aggr.)	2.7	Lamellar
Talc	Silicate	Pale green, grey, white	White	Translucent	Pearly	1	Massive
Magnetite	Fe₃O₄	Black	Black	Opaque	Metallic	5.7	Massive
Hematite	Fe₂O₃	Reddish grey	Red	Opaque	Metallic	6	Tabular
Cinnabar	HgS	Vermilion	Bright red	Opaque	Adamantine / Dull metallic (aggr.)	2.2	Massive
Pyrite	FeS₂	Pale golden	Black	Opaque	Metallic	6.5	Cubes, pentadodecahedrons
Graphite	C	Drak grey	Black	Opaque	Dull metallic	1.7	Foliated
Calcite	CaCO₃	Colourless, white...	White	Translucent	Vitreous	3	Rhombohedrons
Halite	NaCl	Colourless	White	Translucent	Vitreous	2.5	Cubic crystals

External Links

General

How do crystals grow?Visualize how crystals grow at Exploring Earth online book.

Mineral identification.After a good introduction to what minerals and their properties are, the site helps you to identify mineral samples step by step.

Mineral picture gallery.Mineral picture gallery at About.com. With photos and basic data.

Alphabetical listing of mineral species.Everything you ever wanted to know about minerals. With images and lots of data of each species.

The mineral and gemstone kingdom.Another vast resource on minerals: data sheets for many species, photo gallery, gemstones, properties, collecting and more.

Observe common objects made of minerals.Visualize common minerals and objects made of them at Exploring Earth online book.

Images

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