Minerals and Rocks

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In geology, a substance is considered a mineral if it meets the following requirements:
➢ naturally occurring: that people did not make it. (Steel is not a mineral because it is an alloy
produced by people.)
➢Inorganic: hat the substance is not made by an organism. (Wood and pearls are made by organisms and
thus are not minerals.)
➢Solid: that it is not a liquid or a gas at standard temperature and pressure. (Water is not a mineral
because it is a liquid.)
➢definite chemical composition: that all occurrences of that mineral have a chemical composition that
varies within a specific limited range. (The mineral halite (known as "rock salt" when it is mined) has a
chemical composition of NaCl.)
➢ordered internal structure: that the atoms in a mineral are arranged in a systematic and repeating
pattern. (Halite is composed of an equal ratio of sodium and chlorine atoms arranged in a cubic pattern.)

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Because of the limited number of elements present in the Earth’s crust there are only about 3000
minerals known. Only two to 30 of these minerals are common. The most common mineral are
those based on Si and O known as silicates.

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Classification of Minerals According to Chemical Composition

1. Silicates – minerals containing the two most abundant elements in the Earth’s crust, namely, silicon
   and oxygen. Over 90% of rock-forming minerals belong to this group.
2. Oxides – minerals composed of oxygen anion (O2 - ) combined with one or more metal ions
3. Sulfates – minerals containing sulfur and oxygen in the form of the (SO4) - anion
4. Sulfides – minerals containing sulfur and a metal; some sulfides are sources of economically
   important metals such as copper, lead, and zinc.
5. Carbonates – minerals containing the carbonate (CO3)2 - anion combined with other elements

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6. Native Elements – minerals that form as individual elements
   ➢ Metals and Intermetals – minerals with high thermal and electrical conductivity, typically with
   metallic luster, low hardness (gold, lead)
   ➢ Semi-metals – minerals that are more fragile than metals and have lower conductivity (arsenic,
   bismuth)
   ➢ Nonmetals – nonconductive (sulfur, diamond)
7. Halides – minerals containing halogen elements combined with one or more metals

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Formation of Minerals Minerals may be formed by four general processes, they are as follows: ➢Sublimation- This process is comparatively rate. In volcanic eruptions, minor amounts of certain minerals may form from gases escaping from vents of fumaroles. The only common example of sublimation is in relation to volcanoes.

➢Aqueous Solutions- Is the source of important minerals. Dissolved materials may be precipitated from solution by several process:

a.evaporation of the solvent

b.decrease in temperature and pressure

c. loss of carbon dioxide

d.action organism

➢Crystallization from Magma- At moderate depths in the earth’s crust, previously existing rocks may be melted. This molten rock (magma) tends to work its way upward. If it reaches the surface there will be volcanic eruption or lava flow.

➢Contact Metamorphosis- Adjacent to the ascending magma, the country rock may be profoundly changed by the heat and by chemical reaction with the magma.

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Formation of Minerals
Minerals may be formed by four general processes, they are as follows:
➢Sublimation- This process is comparatively rate. In volcanic eruptions, minor amounts of certain
minerals may form from gases escaping from vents of fumaroles. The only common example of
sublimation is in relation to volcanoes.

➢Aqueous Solutions- Is the source of important minerals. Dissolved materials may be precipitated from solution by several process:

a.evaporation of the solvent
b.decrease in temperature and pressure
c. loss of carbon dioxide
d.action organism

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➢Crystallization from Magma- At moderate depths in the earth’s crust, previously existing rocks may be melted. This molten rock (magma) tends to work its way upward. If it reaches the surface there will be volcanic eruption or lava flow.

➢Contact Metamorphosis- Adjacent to the ascending magma, the country rock may be profoundly
changed by the heat and by chemical reaction with the magma.

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