Properties of Minerals Chapter 2.1

What is a mineral? For something to be a mineral it must consist of the following: – It must be naturally occurring – It must be inorganic – It must be a solid – It must be a crystal structure – It must have a definite chemical composition

Inorganic: This means that a mineral cannot form from materials that once were part of a living thing.

Solid: A mineral is always a solid with a definite volume and shape. The particles are packed together very tightly so they cannot move like particles that make up a liquid.

Crystal Structure: The particles of a mineral line up in a pattern that repeats over and over. This repeating pattern in a mineral is called a crystal. A crystal has flat sides called faces that meet at sharp edges and corners.

Definite chemical composition: A mineral always contains certain elements in definite proportions. Almost all minerals are compounds. This means that they usually contain more than one element that differ greatly from the properties of the element it forms.

Identifying Minerals: Geologists have identified about 3,800 minerals Each mineral has characteristic properties that can be used to identify it.

Ways to identify minerals: Color Streak Luster Density Hardness Crystal Systems Cleavage and Fracture Special Properties

Color: Color can be easily observed, but don’t be fooled! See three examples on pg. 46

Streak: A streak of a mineral is the color of its powder. You can observe a streak by rubbing a mineral against a piece of unglazed tile. See example at top of page 47

Luster: Luster is the term used to describe how light is reflected from a mineral’s surface. Minerals are often shiny, others are pearly, waxy, or earthy.

Density: Each mineral has a characteristic density (remember that density is the mass in a given space, or mass per unit volume) Although you can often judge density by the feel in your hand, geologists use a balance to measure density Density = mass/volume

Hardness: In 1812, Friedrich Mohs invented a test to describe the hardness of minerals. This is called the Mohs hardness scale. It ranks ten minerals from softest to hardest. Hardness can be determined through a scratch test. See example on bottom of pgs

Crystal Systems: The crystal’s of each mineral grow atom by atom to form that mineral’s crystal structure. Geologists classify these structures into six groups based on the number and angles on the crystal faces

Cleavage and Fracture: The way a mineral breaks apart can help to identify it. A mineral that splits easily along a flat surface has the property of cleavage. Most minerals do not split apart easily. Fracture describes how a mineral looks when it breaks apart in an irregular way.

Special Properties: Some minerals can be identified by special physical properties. Ex. Magnetism occurs naturally in a few minerals Ex. Minerals that glow under ultraviolet light have a property known as fluorescence.

ASSIGNMENT: Complete numbers 1-2 at the bottom of page 52. Always answer in complete sentences never write out the question.