Specific Gravity Testing Part 1: Definitions
Learn specific gravity testing methods for gem identification. Our 5-part introductory series starts with the basics and key definitions.
2 Minute Read
Before getting into the details of techniques and equipment, some terms must be defined.
What is Specific Gravity?
Specific gravity is also known as relative density or just density. Density is mass per unit of volume or the ratio of the amount of matter in an object to its volume. For example, if you had a piece of plastic and a piece of lead the same size, the lead would be much heavier. That is an illustration of density, how much something weighs in relationship to its size.
Specific gravity is a case of relative density, which is defined as the ratio of the density of one substance to that of another. For gemologists, specific gravity is the relationship of the weight of a gemstone to an equivalent volume of water. When you read that a gem has a specific gravity of 3, it means that the gem weighs three times as much as the same amount of water.
The distinction between density and specific gravity is important in some sciences, but in gemology the terms are interchangeable. For example, it's acceptable to say that a gem has either the specific gravity or density of 3.
How Do You
International Gem Society
Identifying Inclusions Found in Natural Gems
Distinguishing Common Jade Lookalikes
Specific Gravity Testing Part 5: Using Heavy Liquids
Ultraviolet Testing and Gemstone Identification
Why are Topaz and Citrine Gemstones Misidentified?
Identifying Garnets Simplified
Staurolite Value, Price, and Jewelry Information
Amethyst Buying Guide
When you join the IGS community, you get trusted diamond & gemstone information when you need it.
Get started with the International Gem Society’s free guide to gemstone identification. Join our weekly newsletter & get a free copy of the Gem ID Checklist!