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Iron XD
A mineral's color may be influenced by inclusions of other elements or minerals, or even exposure to heat, light, and radiation. A more reliable identification based on color would be the streak, or color of the powdered mineral.
Rubies are made of corundum (aluminum oxide, Al2O3) with trace impurities that give them their color.
The answer is: small amounts of different elements
Pure quartz is a colorless mineral, and so a pure quartz sandstone will appear white due to multiple reflections and refractions between grains. However, impurities in the sandstone may give it some other color. What color it turns out as depends on the impurities. For example, iron oxide will produce a red sandstone.
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Iron XD
Iron XD
The 'streak', or powdered mineral, will not always match the specimen's observed color.
A sapphire gem is mainly composed of the mineral corundum and other trace mineral impurities that give it its color.
A mineral's color may be influenced by inclusions of other elements or minerals, or even exposure to heat, light, and radiation. A more reliable identification based on color would be the streak, or color of the powdered mineral.
The color, luster, and crystal shape of a mineral may be observed just by looking at the mineral. Some minerals have very distinctive colors that help identify them. Although the color of a mineral can give away its identity, color is the least useful property for mineral identification.
Rubies are made of corundum (aluminum oxide, Al2O3) with trace impurities that give them their color.
Sapphire is made of the mineral corundum (aluminum oxide) with impurities to give it color.
The answer is: small amounts of different elements
Staphylococcus aureus is negative for motility, and positive for the indole production. The SIM test tests for sulfur reduction, indole production and motility. Positive for indole production means tryptophan is broken down into indole and pyruvate and will give a red color. Motility, you will see the bacteria move outside of the stab. Positive for sulfur reduction will give a black color in the medium.
Pure quartz is a colorless mineral, and so a pure quartz sandstone will appear white due to multiple reflections and refractions between grains. However, impurities in the sandstone may give it some other color. What color it turns out as depends on the impurities. For example, iron oxide will produce a red sandstone.