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The planet we live on: The beginnings of the Earth Sciences

The planet we live on: The beginnings of the Earth Sciences

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Calcite, CaCO 3 - usually white or colourless, can form good‘dog tooth’ crystals, good cleavage, fairly low hardness, reactswith dilute acid, is <strong>the</strong> main mineral in marble and insome sedimentary rocks (limest<strong>on</strong>e) and is found as a ganguemineral in veinsDiam<strong>on</strong>d, C - usually colourless, forms good crystals, extremelyhard, rareFeldspar, silicate - white or pink, can form good rectangularcrystals, good cleavage, hard, comm<strong>on</strong> in igneous and somemetamorphic rocksGarnet, silicate - usually red or pink, <strong>of</strong>ten forms ball-shapedcrystals, no cleavage, hard, found mainly in medium and highgrade metamorphic rocksGold, Au - gold colour, usually irregular shape, feels verydense, low hardness (s<strong>of</strong>t), rare. <str<strong>on</strong>g>The</str<strong>on</strong>g> picture shows a veryunusual example <strong>of</strong> a large gold nugget, rounded because itwas found in stream sediment.Figure 1.14: Some important minerals and <strong>the</strong>ir identificati<strong>on</strong> properties9

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