Rocks and Minerals_Assignment_S23.docx

LAB 1: ROCKS AND MINERALS 100 points Due at the beginning of lab next week. LEARNING OUTCOMES At the end of this lab, you will be able to: 1. Understand the difference between a rock and a mineral 2. Identify the 3 different rock groups 3. Evaluate physical characteristics unique to the three rock groups INTRODUCTION A mineral is a naturally occurring, homogenous, crystalline solid that has a definable chemical composition. A mineral usually has the same composition and structure throughout. Liquids and gases are not minerals. Geologists use the word “grain” to define any small, natural solid particle. Some grains are crystals that grew into their present shape, but others are pieces of larger crystals, fragments containing many tiny crystals, or even shards of glass. Crystal faces are distinctive geometric shapes defined by smooth, flat, surfaces. Each face forms at a specific angle relative to its neighbor. We organize minerals based on their color, streak, luster, hardness, specific gravity, fracture, cleavage, and special properties. Rocks are a collection of minerals that are held together in a firm, solid mass. Igneous rocks form when molten rock (magma or lava) cools and solidifies. Sedimentary rocks originate when particles are cemented together, or by precipitation of minerals from water. They often accumulate in layers. Metamorphic rocks result when existing rocks are changed by heat, pressure, or reactive fluids. Each of these types is part of the rock cycle. Through changes in conditions, one rock type can become another rock type. The minerals in a rock may be so tiny that you can only see them with a microscope, or they may be as big as your finger. Many rocks are made of minerals containing silicon and oxygen, the most abundant elements in the Earth’s crust. Rocks are identified primarily by the minerals they contain and by their texture. The following tables and charts will help you identify different rock groups and types of rocks within each group.

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Igneous rocks Reference Tables for Physical Setting/EARTH SCIENCE (2011) Property Definition How to evaluate Grain Size Mineral/crystal size Glassy (non-crystalline), fine (cannot see grains), coarse (large mineral grains) Color Reflected visible light Light, intermediate, or dark Vesicles Voids from air bubbles Open voids permeate rock Dark Minerals Estimate % of blackish crystals

Metamorphic rocks Referenc e Tables for Physical Setting/EARTH SCIENCE (2011) Property Definition How to evaluate Banding Foliated rock layering characteristic shape Look for layering in the rock, usually different colors. Can be linear (straight) or distorted (wavy) Grain size Dimensions of minerals/rock building blocks Fine to coarse (if grains exist)

Sedimentary rocks Refer ence Tables for Physical Setting/EARTH SCIENCE (2011) Property Definition How to evaluate Clastic Obvious pieces of rocks (clasts) fused into a matrix Observe clast size, mixture (many sizes), coarse, medium (sand), fine (smooth) Chemical origin Formed in place by chemical processes Results in a uniform mineral throughout. Crystalline texture can range from coarse (visible) to fine. Organic origin Formed in place by biological processes Contains fossils (limestone) or black plant material, such as coal or lignite.

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