Geology - The Earth's Components - Quick Guides | Geology

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Study GuideGeology–The Earth's Components1. Mineral ProperƟesAt first glance, many minerals can look very similar. Because of this, geologists do not rely onappearance alone. Instead, they identify minerals using a set ofspecific propertiesthat are easy totest in the field or in a laboratory. Each property gives an important clue about what the mineral is.1.1 HardnessHardnessdescribes how easily a mineral can be scratched. Geologists measure hardness using theMohs hardness scale, which ranks minerals from1 (softest)to10 (hardest).•Talcis the softest mineral (hardness of 1).•Diamondis the hardest mineral (hardness of 10).In practice, geologists use simple tools to test hardness:•Aknife bladehas a hardness of about5.○If a mineral scratches the knife, it is harder than 5.○If the knifescratches the mineral, its hardness is less than 5.•Athumbnailhas a hardness of about2.5.Because the scale can be hard to memorize, many geologists use amnemonicto remember theorder of minerals on the Mohs scale.

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Study Guide1.2 Color and StreakColoris usually the first thing people notice, but it can be misleading. The same mineral may appearin different colors due to impurities or chemical weathering.A more reliable test is thestreak:•When a mineral is scraped across a porcelain surface called astreak plate, it leaves behinda powdered line.•This streak color is often more consistent and more useful than the mineral’s outer color.1.3 LusterLusterdescribes 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 shinyLuster helps narrow down mineral choices quickly.

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Study Guide1.4 Crystal FormSome minerals grow into clear, recognizable shapes calledcrystal forms. These shapes reflect themineral’s internal atomic structure.Crystal forms develop best when mineralscool slowlyfrom a liquid or fluid, giving atoms time toarrange themselves into orderly patterns.1.5 CleavageCleavageis the tendency of a mineral to break alongflat, smooth planeswhere atomic bonds areweaker.•Some minerals break into cubes, sheets, or other predictable shapes.•Theangles between cleavage planesare 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 ProperƟesGeologists 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 magnet2.The Rock CycleTherock cycleexplains how rocks are continuously formed, changed, and recycled over time. It isnot a straight path with a beginning or an end. Instead, it is an ongoing cycle driven by Earth’s internalheat and surface processes.

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