Properties of Minerals Geologists use characteristics to tell one mineral from another

Mineral Properties we will study Luster Hardness Cleavage Streak DENSITY Color Fracture

Color 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.

A mineral can be many different colors. Below is Mica.

Many minerals can be the same color. Below are gold colored minerals. Which one is gold?

The answer… None of them were real gold.

Luster Refers to the way light reflects from the surface of the mineral. There are two types of luster, –Metallic: looks like polished metal. –Nonmetallic: does not look like polished metal. Nonmetallic can be shiny or dull.

Pyrite has metallic luster

Quartz has nonmetallic luster

Streak When a mineral is scratched along a ceramic streak plate it may leave a specific streak of color. Red chalk on a chalk board makes red marks. White chalk makes white marks. Not all minerals work this way. When some minerals are scratched along a ceramic streak plate, it creates a different color.

Gold When gold is run across a streak plate it makes a yellowish-gold color. That makes sense.

Pyrite or “Fool’s Gold” When pyrite is run across a streak plate, it has a black or dark green streak. Pyrite is not worth much money, while gold is worth a lot. They look alike, so miners call it fool’s gold.

Hematite Hematite’s color is grey, but its streak is red. Hema means blood. The mineral was named hematite because it looked like it was bleeding when it was taken across a streak plate.

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

Cleavage The tendency of a mineral to break along flat surfaces. Some minerals split easily along a flat surface. Not all minerals have cleavage.

Mica has cleavage in one direction. It breaks along one line.

Feldspar has two lines of cleavage. It breaks along two lines.

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

Hardness The resistance to being scratched. Is measured by how easy it is to scratch. Geologists order the hardness by… 1.Scratched by a fingernail. 2.Scratched by a penny. 3.Scratched by a nail. 4.Scratched by a diamond. The Mohs Hardness Scale is used to identify a mineral’s hardness.

Gypsum is soft, it can be scratched by a fingernail.

Calcite is soft, but a little harder because it cannot be scratched by a fingernail, but it can be scratched by a penny.

Fluorite is harder. It can be scratched by a nail, but not a penny or fingernail.

Diamonds are the hardest mineral, so it scratches every mineral.

Density 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.

Special Properties Some minerals have specific properties Fluorescence: some minerals glow when exposed to ultraviolet light Magnetic: Some minerals are attracted to magnets Acid: Some minerals react with acid by bubbling