Specific gravity is best described as which of the following?

Specific gravity is best described as which of the following?

• A. The measure of light refraction in gemstones
• B. The hardness on Mohs scale
• C. The ratio of weight to the weight of an equal volume of water
• D. The degree of cleavage along a plane

Answer: (C)

Specific gravity measures how dense a gemstone is compared with water. It is defined as the ratio of the gemstone's weight to the weight of an equal volume of water. This makes SG a density-related property that doesn't depend on the stone's size, so a small piece and a large piece of the same material share the same SG. Since water has density 1 g/cm^3, SG tells you how many times denser the gemstone is than water. In practice, you determine SG by weighing the stone in air and then in water to see how buoyancy changes the apparent weight. This helps distinguish stones that look similar but have different compositions; for example, diamond runs around 3.5, quartz about 2.65, and corundum near 4.0. This property is different from light refraction (refractive index), from hardness on the Mohs scale, and from cleavage along a plane.

Specific gravity measures how dense a gemstone is compared with water. It is defined as the ratio of the gemstone's weight to the weight of an equal volume of water. This makes SG a density-related property that doesn't depend on the stone's size, so a small piece and a large piece of the same material share the same SG. Since water has density 1 g/cm^3, SG tells you how many times denser the gemstone is than water. In practice, you determine SG by weighing the stone in air and then in water to see how buoyancy changes the apparent weight. This helps distinguish stones that look similar but have different compositions; for example, diamond runs around 3.5, quartz about 2.65, and corundum near 4.0. This property is different from light refraction (refractive index), from hardness on the Mohs scale, and from cleavage along a plane.