What is a Mineral?
Some Facts about Minerals:
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Minerals are always solids, cannot be liquids and gases.
True minerals are only formed by nature.
Minerals are inorganic, meaning they are NOT made of living things.
Minerals are crystals and normally have the same chemical composition throughout.
Minerals: From the Inside Out
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All minerals are made of one or more of the 92 elements present in the Earth’s crust.
Most minerals are made from compounds of several different elements.
Mineral is also made up of one or more crystals.
Types of Minerals:
Silicate Minerals:
 Silicon and oxygen are the main components of the Earth’s crust (90%) and both elements make up
all silicate minerals.
 Examples:
Feldspar – makes up about 50% of the Earth’s crust and is the main component of most
of the rocks on the Earth’s surface.
Biotite Mica – are shiny and soft, and they separate into sheets when they break.
Quartz – is the basic building block of many rocks. Granite normally has many pieces
of feldspar in it.
Nonsilicate Minerals:
 These minerals do NOT contain silicon and oxygen in them. These minerals are normally made of
elements such as carbon, iron, and sulfur.
 Classes of Nonsilicate Minerals:
Native Elements: composed of only one element. Examples: gold (Au), diamond (C), copper (Cu).
Carbonates: composed of carbon and oxygen. Example: Calcite (CaCO3).
Halides: elements of flourine, chlorine, iodine, or bromine combine with sodium, potassium, or
calcium. Example: Halite – Rock Salt (NaCL)
Oxides: elements of aluminum or iron combine with oxygen. Examples: Magnetite (Fe3O4)
Sulfates: contain sulfur and oxygen. Examples: Gypsum (CaSO4).
Sulfides: contain one or more elements, such as lead, iron, nickel, and combined with sulfur.
Example: Galena.
Minerals are identified by looking at the following:
Color – based on what elements they are made of. Also, impurities cause the varying colors in
a given mineral group.
Luster – way a surface reflects light.
Streak – color of mineral in powdered form. (More reliable then just looking at the color of a
rock.)
Cleavage – is the tendency of some minerals to break along flat surfaces. (Ex: diamond breaks
in four different directions.)
Fracture – tendency of some minerals to break unevenly along curved or irregular surfaces.
(Ex: Conchoidal Fracture makes “curves or swirl marks” in the mineral after it is broken.)
Hardness – mineral’s resistance to being scratched. (Moh’s Hardness Scale – See Mineral
Information Sheet.)
Density – measure of the amount of matter there is in a given amount of space.
Special Properties – Fluorescence is when a mineral glows under ultraviolet light (fluorite and
calcite). Some minerals will “react” when they are placed in a weak acid (Ex: Calcite).