The volume of the gold ball is 0.52 cubic centimeter and the volume of the silver ball is 0.95 cubic centimeter (volume is mass divided by density).įrom this we can conclude that the silver ball will displace 0.95 cubic centimeter of water, which weighs 0.95 gram. Through some simple math we can calulate the volume of the balls. Water has a sg of 1, so the weight of a cubic centimeter of water is 1 gram (actually 0.0098 Newton, but grams used for simplicity). When you hang both balls in water (immersed), then the silver ball will displace much more water than the golden ball due to its higher volume. In other words, the gold ball will have a smaller volume than the silver ball. The gold ball has a sg of 19.3, while silver has a sg of 10.5.īecause gold has a sg that is almost twice as much as silver, you can imagine that the 10 gram gold ball will be smaller than the 10 gram silver ball. This may sound complicated but it is a fairly simple, yet brilliant, law.Ĭonsider two balls of equal weight but of different specific gravity, for instance a 10 gram gold ball and a 10 gram silver ball. In gemology, specific gravity is, usually, determined through an apparatus based on Archimedes' Principle.Īrchimedes' Principle (or the Law of Buoyancy) states that: the upward force on an immersed object is equal to the weight of the displaced fluid. For instance, the SG of Diamond = 3.52 (whereas the density of Diamond = 3.52 g/cm³). Since specific gravity is relative to the weight of an object in air and its weight in water, it is a ratio and isn't expressed in units (such as kg/m³). Room temperature conditions are adequate for gemological purposes, as the small difference in density of the water will have little effect on the readings (measured to the second decimal). By convention, the temperature of the water is 4° C and at standard atmosphere because the density of water is greatest under these conditions. Specific gravity (also known as 'relative density') is the ratio between the weight of a stone in air and the weight of an equal volume in water. 2 Specific Gravity of Some Common Gem Minerals.