Minerals Mandy Meeks Baldwin Arts and Academics Magnet School © Fabre Minerals

What is a mineral?

A mineral is a naturally occurring, inorganic substance with a definite chemical composition and the orderly arrangement of atoms. There are 4000 different minerals on Earth. Olivenite © D. Schläfli

The 4 Properties of Minerals: 1. All Minerals are formed by natural processes. Baryte © Daniel Ozdín

The 4 Properties of Minerals: 2. They aren’t made by life processes Muscovite © Rob Lavinsky

The 4 Properties of Minerals: 3. Minerals have a “definite composition"  ex: every molecule in table salt is Sodium Chloride, NaCl Azurite Photo Copyright © Flavio Giuseppe Taricco

The 4 Properties of Minerals: 4. All minerals are crystalline solids. Natropharmacoalumite Photo Copyright © Christian Rewitzer

Structure of Minerals Minerals are crystals A crystal is a solid in which the atoms are arranged in orderly, repeating patterns. Autunite, Rockbridgeite Photo Copyright © Volker Betz

Examples of Crystal Structure

Shapes of minerals see p. 64 in textbook Mineral ShapePictureExample Cubichalite Monoclinicgypsum Triclinicfeldspar TetragonalZircon Hexagonalquartz Orthorhombicsulfur

Forming Minerals Crystals can form from magma, or hot melted rock. Crystals can also form from minerals dissolved in water. Pahoehoe lava, cooling in lava ropes in Hawaii. The mineral Calcium Carbonate (Calcite) is deposited from water dripping in caves, forming stalactites and stalagmites.

Halite Halite is a mineral that forms from water evaporating from the sea. It is commonly known as rock salt. The chemical composition of halite is sodium chloride. Halite deposits in the Dead Sea.

Following the guideline her life depends on, a diver threads the needle through a stalagmite forest in Dan’s Cave on Abaco Island in the Bahamas. A single, misplaced fin kick can shatter mineral formations tens of thousands of years old Photograph by Wes C. Skiles

Mineral Identification

Mineral Appearance:  Can use color and appearance to identify minerals.  Appearance is not enough to identify minerals- some minerals look just alike!  Example: Pyrite (Fool’s Gold) and Gold.

Luster The way a mineral reflects light is known as luster. Metallic luster shines like metal. Nonmetallic luster does not shine like metal.  Ex: dull, pearly, silky, and glassy. Annabergite

Hardness A measure of how easily a mineral can be scratched is hardness. Mohs scale of hardness: ranges from 1 to 10.  1 = softest. Ex: Talc  10 = hardest Ex: Diamond.  Can use the known hardness of common objects to determine the hardness of an unknown mineral.  Once you have determined the hardness of the mineral, you can identify it.

Specific Gravity The specific gravity is the ratio of the weight of the mineral compared to the weight of an equal volume of water. Ex: Gold has a specific gravity of 19, so it is 19 times heavier than water. Pyrite has a specific gravity of 5, so it is 5 times heavier than water.

Streak When you rub a mineral across a piece of unglazed porcelain tile, a streak of powdered mineral is left behind.  Streak is the color of the mineral in powdered form. Can only test minerals that are softer than the streak plate. Some minerals are so soft you can streak them on paper, like the graphite in your pencil!

Cleavage and Fracture Cleavage is when a mineral breaks along a smooth, flat surface.  Determined by the arrangement of atoms in the mineral.

Cleavage and Fracture Fracture is when minerals break along uneven surfaces.

Uses of Minerals

Gems Gems are rare and beautiful minerals. Most gems are similar to common minerals, but have small differences that make them clearer, brighter, or more colorful. See P. 74 in your book

Ore A mineral or rock that contains a useful substance that can be mined at a profit.

Vein Minerals Sometimes metallic elements dissolve in fluids. The fluid forms mineral deposits in the cracks between rocks- this is a mineral vein. Gold Vein

Silicates Minerals that contain silicon (Si) and Oxygen (O) Silicon and Oxygen are two of the most abundant elements in Earth’s crust. Examples of Silicates: Feldspar and Quartz. Quartz, Dauphine, France