Minerals and Their Properties

A mineral is an inorganic solid that occurs naturally and has a definite chemical composition and structure.

Exist in nature as a solid Uniform chemical composition Minerals must meet the following criteria: Occur naturally Inorganic Exist in nature as a solid Uniform chemical composition Crystalline structure

A mineral can usually be identified by its physical properties. These physical properties include: Color Streak Luster Density Crystal shape Hardness

COLOR The color depends on whether other substances were present when the mineral formed. Ex. Quartz is often clear, but it can be purple, pink, or gray Topaz can be yellow, pink, or blue

STREAK Is the color of a mineral in its powder form. If you rub a mineral across a porcelain tile called a streak plate, it may leave a stripe of color. Ex. Pyrite looks golden, but it leaves a greenish-black streak

LUSTER Is the way a mineral reflects light. Common adjectives that describe luster include dull, shiny, greasy, pearly, metallic, and glassy. Ex. Garnet - glassy Pyrite – metallic Talc - greasy

DENSITY Is the mass of a sample of a substance divided by its volume. D=mass/volume Density is measured in grams per cubic centimeter (g/cm3). Different minerals have different densities.

CRYSTAL SHAPE Crystal shapes are classified according to six crystal systems. The way the crystals form and are arranged causes some minerals to break more easily in one direction than another. If a mineral breaks regularly along a flat surface, it is said to have CLEAVAGE. If the mineral breaks irregularly, it is said to FRACTURE.

6 CRYSTAL SYSTEMS

Each mineral has a distinct hardness that ranges from very soft to very hard. Friedrich Mohs developed a hardness scale based on ten relatively common minerals. The MOHS SCALE ranks the hardness of minerals from 1 to 10, with 1 being the softest (talc) and 10 being the hardest (diamond).