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Geology - The Earth's Components

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    Study Guide Geology – The Earth's Components 1. Mineral Proper Ɵ es At first glance, many minerals can look very similar. Because of this, geologists do not rely on appearance alone. Instead, they identify minerals using a set of specific properties that are easy to test in the field or in a laboratory. Each property gives an important clue about what the mineral is. 1.1 Hardness Hardness describes how easily a mineral can be scratched. Geologists measure hardness using the Mohs hardness scale , which ranks minerals from 1 (softest) to 10 (hardest) . • Talc is the softest mineral (hardness of 1). • Diamond is the hardest mineral (hardness of 10). In practice, geologists use simple tools to test hardness: • A knife blade has a hardness of about 5 . ○ If a mineral scratches the knife, it is harder than 5. ○ If the knife scratches the mineral, its hardness is less than 5. • A thumbnail has a hardness of about 2.5 . Because the scale can be hard to memorize, many geologists use a mnemonic to remember the order of minerals on the Mohs scale.

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    Study Guide 1.2 Color and Streak Color is usually the first thing people notice, but it can be misleading. The same mineral may appear in different colors due to impurities or chemical weathering. A more reliable test is the streak : • When a mineral is scraped across a porcelain surface called a streak plate , it leaves behind a powdered line. • This streak color is often more consistent and more useful than the mineral’s outer color. 1.3 Luster Luster describes how light reflects off a mineral’s surface. Common types include: • Metallic – shiny like metal • Glassy (vitreous) – looks like glass or glazed porcelain • Earthy – dull and not shiny Luster helps narrow down mineral choices quickly.

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    Study Guide 1.4 Crystal Form Some minerals grow into clear, recognizable shapes called crystal forms . These shapes reflect the mineral’s internal atomic structure. Crystal forms develop best when minerals cool slowly from a liquid or fluid, giving atoms time to arrange themselves into orderly patterns. 1.5 Cleavage Cleavage is the tendency of a mineral to break along flat, smooth planes where atomic bonds are weaker. • Some minerals break into cubes, sheets, or other predictable shapes. • The angles between cleavage planes are often unique and can help identify mineral groups. • A hand lens or magnifying glass is often enough to see cleavage in the field. 1.6 Other Useful Proper Ɵ es Geologists may also use additional traits to identify minerals, such as: • Fracture – how a mineral breaks if it does not cleave (for example, curved or jagged breaks) • Specific gravity – how heavy the mineral feels for its size • Magnetism – whether the mineral is attracted to a magnet 2. The Rock Cycle The rock cycle explains how rocks are continuously formed, changed, and recycled over time. It is not a straight path with a beginning or an end. Instead, it is an ongoing cycle driven by Earth’s internal heat and surface processes.

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