What are minerals?
Minerals are the building blocks of the earth’s crust. Any material is called a mineral only if it qualifies the following all points.
- It must be naturally formed. The minerals which are made in the laboratory are not qualified as minerals. However, the minerals that are made in the laboratory but are not found in nature, can be qualified as minerals.
- It must be made of inorganic matter. Also it is solid.
- It must have a specific chemical composition. It is represented by a chemical formula.
- It has a crystalline form. Crystalline form is an internal structure which they create when they are joined in a certain order.
Let’s understand the mineral by example of diamond. Diamond is a mineral because it is naturally formed, it is made of carbon, it is a solid, and it has a regular geometric array of carbon atoms.
On the other hand, coal is not a mineral but it is a rock. Because it is organic material which is formed from the remains of animals and plants. Also, Coal does not have a specific composition and crystal structure.
How do minerals form?
Minerals form under specific conditions, especially at the right temperatures and pressures. In most cases, mineral formation depends on the rock family either they are igneous, sedimentary, or a metamorphic rock.
In general, igneous minerals crystallize from molten rock at high temperatures and at about 30 Km deep. For example quartz or biotite mica. Sedimentary minerals form through the evaporation of water, precipitation from water, or through the deposition of such hard parts as bones or shells of organisms. For example, halite, chert, carbonate, and aragonite. Metamorphic minerals form when minerals within rocks recrystallize in response to changes in heat and pressure.
Examples of Common minerals
It is the most common mineral of the rocks. About half of the earth’s crust contains this Feldspar. Feldspar is the various aluminosilicate of potassium, sodium, calcium, and barium.
Basalt, Dolerite, Gabbro, etc rocks are composed of pyroxene groups. Pyroxene crystals are prismatic in shape. Rocks made of pyroxene minerals are called pyroxenes.
Quartz is the second most found mineral in the earth’s crust. The word quartz derives from the German word ‘Quartz’ which means ‘hard’. It’s the main ingredient of soil and granite. In its purest form, quartz is colorless which is often called rock crystal or mountain crystal. The colors in other quartz crystals are caused by impurities within the molecular structure of the mineral.
Mica can be cut into a very thin layer. Mica crystals are heat resistance and do not conduct current. It’s mostly found in igneous and metamorphic rocks. Mica is a very complex compound of silicate and it’s unaffected by acid.
Olivine is a magnesium iron silicate. Olivine is found all over the earth and also found in a meteorite.
Physical properties of minerals
Minerals are identified based on the different physical properties such as composition, crystal structure, luster, colour, and hardness.
There are many properties of minerals that give them colours, such as different impurities in minerals, mineral composition (chemistry of minerals) and minerals that create colors by light interference.
Many minerals have a distinctive colour and some minerals have a wide variety of colours. For example, minerals such as olivine (green), biotite (black), malachite (green), and azurite (blue) have definitive colour. On the other hand quartz can be found in many colours such as white, colourless, yellow, gray, pink, black, and purple. So on the basis of colour, it is difficult to identify minerals.
Hardness is a distinctive property of minerals that refers to resistance of a mineral to being scratched. To determine hardness, rub the surface of the minerals with an object of known hardness. Talc is the softest mineral and diamond is the hardest mineral. The Mohs hardness scale was developed by Friedrich Mohs in 1822 as a diagnostic tool. This scale is divided into 10 steps , each marked by a common mineral. The scale represents that any mineral on the scale will scratch all other minerals on the scale that have a lower number.
A luster of minerals is the amount and quality of light reflected from their surface. The luster of most metallic minerals is metallic and the luster of non-metallic minerals is non-metallic. Non-metallic luster can be of many types, such as diamondsome, pearl sum, resinous, cachopam (like glass or broken glass), such as in quartz. Fibrous minerals have silky luster. Conversely some minerals do not have luster, such as kaolinite.
4. Cleavage and fracture
Most minerals break easily in special conditions and their surface remains smooth and flat when broken. This property of minerals is called Cleavage. This is because in some minerals the bonds between the layers of atoms aligned in a certain direction are weaker than bonds between other layers. Cleavage can occur in many directions, such as in mica occur in one direction, in felspar in two directions, in calcite in three directions, and in sphalerite in four directions.
When minerals are broken in any direction other than the cleavage surface, they are called fractures. Fractures are generally rough or irregular and thus appear duller than cleavage surfaces.
The color of the mineral in its powdered form is called a streak, which may or may not be the same color as the mineral. Streak is most important when identifying metallic minerals, especially non native metals. For example, the streak of gold is metallic yellow. And for pyrite the streak is dull black.
6. Specific gravity
The specific gravity of a mineral is actually the weight of that mineral divided by the weight of an equal volume of water. The relative gravity of minerals is fixed, but for minerals whose compound is not constant, it changes along with the relative gravity compound.
Apart from these, magnetism, Effervescence, Fluorescence, taste, feel, and odor are other properties of minerals.