Specific Gravity

Abstract: Gemology is the science of dealing with natural, synthetics and stimulants of diamonds, pearls and other precious stones, gemstones or colored stones as they are called in the United States.

I have put up a few posts on gemology and will put up more posts later. All are written in as simple lay man terms as possible. An understanding on some basic gemology fundamentals will enable one to appreciate more on diamonds and colored stones. It will also give you some perspective when you read a gemlab report on a colored stone.


Every natural mineral has a different density. If the particles are packed very close together and are arranged in a very orderly manner, then more particles will be able to fill into a given volume. This would give you the mass of the mineral, which quantifies the amount of matter and is expressed in unit grams or kilograms.

Hence, density is a measurement of how much mass is in a given volume.

                    Density = Mass / Volume

Or gm/cm3 as measured in the metric system

The density of water at temperature of 4oC is 1 gm/cm3.  

The density of gold is 19.3 gm/cm3. That is, gold is 19.3 times heavier than water.

Specific Gravity

SG is the comparison of the weight of a specific mineral to the weight of an equal volume of water. Hence, specific gravity is the ratio of the density of a mineral to the density of water.

Since this is a ratio, specific gravity is an absolute number.

Hence, specific gravity of gold = Density of gold / density of water = 19.3

The specific gravity of a gemstone provides valuable information on its identity. SG seldom overlaps and is quite a fairly constant.

One of the method of determining the SG of a gemstone is by using the hydrostatic balance. The gemstone is weighed in air and weighed in water by totally immersing the subject specimen in it.

In later posts, I shall share my experience by using SG to identify jade or colored stones.

Photo credit: mineralab.com, theengineeringmindset.com



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