Properties of Minerals

What are minerals? There are over 3000 minerals. Roughly 100 common minerals A mineral is a naturally occurring, inorganic solid that has a crystal structure and definite chemical composition.

5 Characteristics of Minerals Naturally Occurring Inorganic Solid Crystal Structure Definite Chemical Composition

Naturally Occurring Formed by geological processes not man. Ex: Copper is a mineral but steel is not because it is made by man.

Inorganic A mineral cannot be made from a material that was once a part of a living organism. Ex: Oil and coal form naturally in the Earth’s crust, but form from the remains of animals and plants from millions of years ago.

Solid A mineral has to be solid with a definite shape and volume. In a solid the molecules are packed tightly so they cannot flow freely, so the object keeps it’s shape.

Crystal Structure A mineral is made up of a pattern that continually repeats The repeating pattern of a mineral’s particles forms a solid called a CRYSTAL. Sometimes you are able to see the crystal with the naked eye other times you must use a microscope. Opal is considered a mineral even though their particles are not arranged in a crystal structure.

Definite Chemical Composition A mineral has a definite chemical composition. Meaning: Minerals contain certain elements in definite proportions. Almost all minerals are compounds: made of 2 or more different elements bonded together. Some minerals are made of one element: Examples are gold, silver, and copper.

Element, Compound, Mixture Mixture: is a substance composed of two or more substances that re mixed together but not chemically. Each substance in a mixture keeps their separate properties. Example: Salt Water Element: a substance composed of one type of atom. Each element has unique chemical and physical properties.

Compound: is a substance composed of two or more elements where the elements no longer have distinct properties. Each compound has it’s own properties that differ from the properties of each element.

Identifying Minerals Gold Rush: COLOR ALONE WILL NOT WORK! Each mineral has its own unique physical properties that can be used to identify it. The following characteristics can be used to identify minerals: Hardness Color Streak Luster Density Crystal Systems Cleavage/Fracture Special Properties

Color Very simply what is the color of the mineral. This can be easily seen however color can only be used to identify a few minerals because only a few minerals have their own characteristic color. For example azurite is always blue. Some minerals like quartz are found in several colors.

Streak The streak of a mineral is the color of its powder. You can determine this by rubbing a mineral against a piece of unglazed tile called a streak plate. The color of a mineral may vary, but its streak will not. Pyrite: Gold color Greenish black streak Gold: Gold color Yellow streak

Luster This term is used to describe how a mineral reflects light from its surface. Minerals containing metals are often shiny. Ex: Galena: Metallic Luster Some of the terms used to describe a non-metallic luster in minerals: Glassy, earthy, waxy, pearly, silky.

Hardness How hard a mineral is an excellent tool for identifying the mineral. MOHS HARDNESS SCALE was invented to test and compare the hardness of different minerals. The scale ranks 10 minerals from softest to hardest.

Hardness (continued) A mineral can scratch any mineral softer than itself and it will be scratched by any mineral harder than itself.

Mohs Hardness Scale Talc 1 1.5 Graphite Gypsum 2 “ 2.5 Fingernail “ Mohs Mineral Hardness Example Other Mineral   Talc 1    1.5  Graphite Gypsum 2  “   2.5 Fingernail “ Calcite 3 Copper coin      Fluorite 4       Apatite 5 Steel nail   5.5 Glass plate   Orthoclase 6    6.5 Steel file  Quartz 7  Garnet    Topaz 8       Corundum 9       Diamond 10  

Density Each mineral has a characteristic Density. Density = Mass / Volume (remember the heart)

Crystal Systems Crystals of each mineral grow atom by atom to form that mineral’s particular crystal structure. There are 6 groups/ mineral structures: Cubic Hexagonal Tetragonal Monoclinic Triclinic Orthorhombic

Cleavage A mineral that splits easily along flat surfaces has this property. Cleavage is determined by the arrangement of atoms inside the mineral. Depending on the arrangement minerals may split more easily in one direction than another.

Fracture Fracture describes how a mineral looks when it breaks apart in an irregular way.

Special Properties Some minerals have special properties such as FLUORESCENCE. These minerals will glow under fluorescent light. Some minerals are magnetic. Ex: Lodestone

Special Properties Calcite fizzes and gives off Carbon dioxide when you drop acid on it. Quartz has electrical properties: If pressure is applied to these crystals a small electrical current is produced. Because of these properties, quartz crystals are used in watches, microphones, etc.