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What is specific gravity or relative density and how it is useful in determining the identity of minerals and other substances. Specific gravity is a property of a mineral and can be used to help identify that mineral however some minerals have the same specific gravity so you can only narrow down to a group of minerals. To narrow down to a specific mineral you have to use other properties like luster, hardness, color, crystal system, streak etc. to identify the mineral.
To determine the specific gravity you need a scale (I use a Sartorius scale with a specific gravity kit that comes at an extra cost) that allows you to weight a sample of a mineral in air and then immersed in distilled water for accuracy. Weight in air – weight in water = mineral volume Density = mineral weight (weight in air)/mineral volume = specific gravity Example The mineral apatite Weight in air = .951 g – weight in water = .660 g = mineral volume = .291 Density = mineral weight (weight in air) = .951 / mineral volume = .291 = specific gravity = 3.2680412 The specific gravity of apatite = 3.35 to 3.10 with a mid range of 3.225 I then use the crystal system to determine the minerals with in that range and because apatite is a hexagonal crystal system I can narrow it down to the mineral apatite
Mineral or metal specific gravity Gold 15.5 – 19.3
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