Limestone is a sedimentary rock that is generally composed of calcium carbonate (calcite). It is mainly formed in clear, warm, and shallow marine waters.
Hornblende can be either a calcium-iron-magnesium silicate, an aluminum-magnesium-iron silicate, or an iron-magnesium silicate. This mineral makes up many igneous and metamorphic rocks.
Amethyst is a purple variation of quartz that gets its color from iron atoms in the crystal matrix.
Obsidian is an igneous rock that forms when molton rock material cools so fast that atoms are unable to form together in a crystalline structure.
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