Mineral IDHow to identify a mineral by its

properties

Introduction Which mineral properties are most important in identification.

Scientists have discovered up to 6000 minerals

Mineral Properties

To meet the definition of "mineral" used by most geologists a substance must meet five requirements:

1.naturally occurring2.inorganic3.solid4.definite chemical composition5.ordered internal crystalline structure

Mineral Property #1 Color & Streak

Color is the first thing someone notices when they view a mineral.

Color is also one of the big reasons that attract people to minerals.

Generally speaking, color is not a good property to be used in the identification of minerals. It is usually the first property to confuse a novice collector into making an incorrect identification.

Many minerals have different colors and some minerals' colors are identical to other minerals' colors.

Mineral Property #1 Color & Streak

Streak is closely related to color, but is a different property because the color of the mineral may be different than the color of the streak.

Streak is actually the color of the powder of a mineral. It is called streak because the proper way to test for streak is to rub a mineral across a tile of white unglazed porcelain and to examine the color of the "streak" left behind.

Mineral Property #1 Color & Streak

Pyrite (known as "Fool's Gold") is always brassy yellow when found in crystals, even broken crystals, of any size; but when powdered, produces a black streak.

Gold's streak, by the way, is yellow!

Hematite's streak is blood-red

Galena's streak is lead gray

Mineral Property # 2Luster A mineral’s luster is the way in which light reflects from the surface.

The two major types of luster are metallic & nonmetallic.

Mineral Property # 2Luster

Some other ways to describe luster are

Dull - just a non-reflective surface of any kind

Earthy - the look of dirt or dried mud Fibrous - the look of fibers Greasy - the look of grease Gumdrop - the look a sucked on hard candy Metallic - the look of metals Pearly - the look of a pearl Pitchy - the look of tar Resinous - the look of resins such as dried

glue or chewing gum Silky - the look of silk, similar to fibrous

but more compact Submetallic - a poor metallic luster, opaque

but reflecting little light Vitreous - the most common luster, it simply

means the look of glass Waxy - the look of wax

Mineral Property # 3How a mineral breaks

When a mineral breaks it does so either by fracturing or by cleaving.

Cleavage is the tendency of a mineral to break along flat surfaces.

Crystal cleavage is a smooth break producing what appears to be a flat crystal face.

Fracture is the tendency of a mineral to break into irregular pieces.

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Mineral Property # 3How a mineral breaks

When a mineral breaks it does so either by fracturing or by cleaving.

Cleavage is the tendency of a mineral to break along flat surfaces.

Crystal cleavage is a smooth break producing what appears to be a flat crystal face.

Fracture is the tendency of a mineral to break into irregular pieces.

Mineral Property #4Hardness A mineral’s hardness is its resistance to being scratched.

A scale known as the Moh’s scale is often use

Mohs Scale of Hardness

Mohs Scale

Rating Type mineral What it can be scratched by…

1 Talc Baby powder

2 Gypsum fingernail

3 Calcite bronze coin

4 Fluorite iron nail

5 Apatite glass

6 Feldspar penknife blade

7 Quartz steel knife

8 Topaz sandpaper

9 Corundum

10 Diamond

Mineral Property #5Density

Each mineral has a specific density. Density is the mass of a given space or in scientific terms the mass per unit of volume.

For example, if you have two minerals of the same size one might be heavier than the other. The galena will be three times heavier than the same size of quartz.

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Mineral Property #5Density

Geologists measure density by the following: First they use a balance to determine the mass of a sample.

Second, they place the mineral in water to see how much water it displaces.

The volume of displace water = the volume of the sample

Third they use the following formula:Density = Mass/Volume