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Diamonds can only form at depths of 100 miles or more below the earth's surface where pressures are a million pounds per square inch and temperatures are above 2,500̊F.╿ How do we get minerals?
Minerals must be mined from the ground, either by surface, underground, or drilling methods.
Slow cooling means the individual mineral grains have a long time to grow, so they grow to a relatively large size.
Intrusive rocks have a characteristically coarse grain size.
Clastic sedimentary rocks may have particles ranging in size from microscopic clay to huge boulders.
Their names are based on their clast or grain size.
This process begins when water traveling through rock dissolves some of the minerals, carrying them away from their source.
Clastic sedimentary rocks are made up of pieces (clasts) of pre-existing rocks.
Metamorphic rocks started out as some other type of rock, but have been substantially changed from their original igneous, sedimentary, or earlier metamorphic form.
Metamorphic rocks form when rocks are subjected to high heat, high pressure, hot, mineral-rich fluids or, more commonly, some combination of these factors.
[Sources: Mostly from USGS, Cliff Notes (Weathering and Soil) and newspaper articles] Geologist classify the Earth's rocks into three categories: 1) igneous, formed by magma within the Earth;.
2) sedimentary, formed when sand, clay or other materials are deposited by water, wind or glacial action and cemented together by pressure and chemical reactions; and 3) metamorphic, sedimentary or igneous rocks that have been later modified by heat and pressure or natural processes. Most gems are crystals formed by the cooling of hot gases, solutions and melts deep inside the earth.