Minerals

Simple Mineral Properties Rocks and minerals are not the same thing. A mineral is a solid, naturally formed inorganic substance that always has the same composition and the same properties. A mineral compares to a rock as a tree compares to a forest. A forest is made up of trees; most rocks are made up of minerals.

Each mineral has its own set of properties, and it can be identified by its properties.

Simple Physical Properties Color Streak Luster Density Hardness Cleavage and Fracture Unique Properties

Color One of the least dependable properties you can use to identify a mineral. Color alone is not reliable. Pyrite Gold

Streak Color of a mineral’s powder when it is rubbed on a rough surface.

Luster Refers to the appearance of a mineral’s surface in light. There are two types; metallic and non metallic Nonmetallic luster can be described using such terms as waxy, pearly, glassy, dull or brilliant.

Cleavage The way a mineral breaks: along a flat surface

Fracture The way a mineral breaks; along a curved surface.

Density A measure of how much matter, or mass, an object contains for its size, or volume. Density doesn’t change with the size of the sample.

Hardness One of the most important properties used to identify minerals. All minerals fall between talc and the diamond. A set standard is used to measure the hardness. A German mineralogist, Friedrich Mohs, devised the scale in 1822.

Mohs Hardness Scale Mineral Rating Testing Method Talc Gypsum Calcite Fluorite Apatite Feldspar Quartz Topaz Corundum Diamond Rating Testing Method 1 Softest known mineral. It flakes easily when scratched by a fingernail. 2 A fingernail can easily scratch it. 3 A fingernail cannot scratch it, but a copper penny can. 4 A steel knife can easily scratch it. 5 A steel knife can scratch it. 6 Cannot be scratched by a steel knife, but it can scratch window glass. 7 Can scratch steel and hard glass easily. 8 Can scratch quartz. 9 Can scratch topaz. 10 Hardest known mineral. Diamond can scratch all other substances.

Unique Properties Magnetism Chemical Properties Reaction to ultraviolet radiation.