Chapter 2.1 What Are Minerals?

What Are Minerals? A MINERAL is a naturally occurring, inorganic solid that has a crystal structure and a definite chemical composition.

Characteristics of Minerals Five Must-Have Characteristics A mineral must be: Naturally Occurring Inorganic Solid Crystal Structure Definite Chemical Composition

Naturally Occurring A mineral must occur naturally. Cement, brick, steel, and glass all come from substances found in Earth’s crust, but they are manufactured by people.

Inorganic Inorganic – the mineral cannot arise from materials that were once part of a living thing. Ex. Coal is NOT a mineral because it is made up the remains of plants and animals.

Crystal Structure What Type of Structure Must It Have? A mineral must have a crystal structure – a repeating pattern of a mineral’s particles that forms a solid. Faces – a crystal’s flat side that meets at sharp edges and corners.

Cinnabar – composed of the elements Mercury and Sulfur Chemical Composition What Type of Composition Must It Have? A mineral must have a definite chemical composition – it always contains certain elements in definite proportions; most minerals are compounds. Cinnabar – composed of the elements Mercury and Sulfur

Element vs. Compound What Is the Difference? Element – a substance composed of a single kind of atom. Ex. Hydrogen Compound – Two or more elements combined so that the elements no longer have distinct properties. Ex. Water H20

Identifying Minerals Identification by Properties Properties: Color (This can vary.) Streak Luster Hardness Density Crystal Shape Cleavage and Fracture Special Properties

Streak What Is the Streak Test? The streak of a mineral is the color of its powder. The streak color and the mineral color are often different. To test: rub a mineral against an unglazed tile (streak plate).

Luster Luster – used to describe how a mineral reflects light from its surface. Minerals containing metals are often shiny. Earthy, waxy, and pearly.

Luster

Luster

Hardness Friedrich Mohs invented a test to describe and compare the hardness of minerals. Mohs Hardness Scale Ranks 10 minerals from softest to hardest.

How Does the Mohs Scale Work? Gypsum (2) will scratch talc (1). Calcite (3) will scratch gypsum (2) Fluorite (4) will scratch calcite (3), etc.

Density Each mineral has a characteristic of density. Density – or mass per unit volume; Density = mass/volume. Displacement – the volume of the displaced water equals the volume of the the sample.

Crystal Structure The Required Shape/Structure Minerals have a crystal structure Cubic Hexagonal Tetragonal Orthorhombic Monoclinic Triclinic

Crystal Structure

Cleavage What Is Cleavage? Cleavage – A mineral’s ability to split easily along a flat surface. The ability to break apart depends on the arrangement of the atoms in the mineral. Cubic Cleavage Basal Cleavage

Mineral Fracture Fracture – How a mineral looks when it breaks apart in an irregular way.

Special Properties Fluorescence – minerals that glow under ultraviolet light. Magnetism - ex. Loadstone Chemical reactivity- ex. Calcite gives off carbon dioxide. Electrical properties – ex. quartz.