There are about 3,000 known minerals, only about 30 are common. The most common are quartz,feldspar,mica, and calcite.
These minerals make up most of the rocks found in the Earth’s crust.
Most of the Earth’s crust is made up of feldspar, followed by quartz and mica.
So what is a mineral? What are the characteristics of all minerals?
What is a mineral? Mineral- A mineral is a naturally formed, inorganic solid with a crystalline structure. Rocks are actually made of many minerals but minerals are not made of rocks.
1. A mineral occurs naturally.
2. A mineral is solid.
3. A mineral has a definite chemical composition.
4. A mineral’s atoms are arranged in an orderly pattern.
5. A mineral is inorganic (was never alive)
To be able to identify these and other minerals, we need to look at the properties used to separate and distinguish these minerals.
Remember!: Rarely is a mineral identified by a single property. These properties need to be considered together to correctly identify a mineral.
Mineral properties ► Color ► Luster ► Cleavage & Fracture ► Streak ► Hardness ► Other
Color is the most easily observed mineral property and the least useful!
Many minerals have a similar color.
Many minerals can turn colors due to impurities. They may also have a mottled appearance or wavy appearance.
For example, pure quartz is colorless or white, impurities can make the mineral rose, purple or pink!
Luster refers to the way a mineral shines in reflected light. Notice the difference between these two minerals?
The mineral on the left has a metallic luster (looks like a metal), the one on the right, a nonmetallic luster (does not look like a metal).
Certain minerals have a metallic luster, such as silver, copper and gold. Minerals that do not reflect light have a nonmetallic luster, and are described by terms like glassy, pearly, dull and silky.
Other terms that might be used include greasy, dull, and earthy.
Streak of a mineral is the color of its powder when rubbed on an unglazed white tile.
The streak is often not the same color as the mineral. A minerals color may vary, but the streak rarely will!
Color of streak. A mineral may not leave a streak.
The cleavage of a mineral is how it breaks.
Cleavage – if it looks like it has been cut, flat surfaces Irregular(Fracture) – does not have a clean break Observations:
Mica is probably the best example as it splits into thin sheets. It is said to have one perfect cleavage.
Feldspar splits readily in two directions, always at or near right angles.
Cleavage & Fracture Best identified on a fracture surface
How resistant the mineral is to being scratched. (scratch test!) Diamond is the hardest of all minerals, and talc is the softest.
Friedrich Mohs devised a hardness scale. In this scale, ten well known minerals are given numbers from one to ten.
Talc (left) is the softest and has a hardness of 1. A soft pencil lead will scratch talc. Gypsum is a bit harder and has a hardness of 2. A fingernail scratches gypsum.
Calcite (left) has a hardness of 3 and a copper penny just scratches it.
Diamond with its hardness of 10 can easily scratch the rest of the minerals.
Use Mohs’ Scale. Does it scratch with a finger nail? Penny? Nail?
Would a fingernail scratch calcite? NO
Would a steel nail scratch orthoclase? NO
Would a copper penny scratch talc? YES
Would a copper penny scratch fluorite? NO
Would a fingernail scratch gypsum? YES
Crystal shape can be a useful property to identify minerals if the minerals have had the time and space to form crystals. Most mineral grains that are found in rocks, lack the room to grow.
Malleable Magnetic Radioactive Flourescence Taste
Halite (rock salt) can be identified by its taste. This practice is not recommended!
This is the state of glowing while under a ultraviolet light. Some minerals even glow once the light is turned off!
Some minerals, such as this uraninite, are radioactive. They give off subatomic particles that will activate a Geiger counter.
Some minerals that contain Iron, are magnetic and can be picked up by a magnet.