 Each of these Gemstone pages is offered to give you useful information on the individual gemstones - from technical data to Ellie's ideas about how she likes to use the stones.
The following are some technical definitions that are used on the individual Gemstone pages:
Specific Gravity: The number of times heavier a gemstone is than an equal volume of water. It is the ratio of the density of the stone to the density of water. You can use specific gravity with other measurements to estimate the carat weight of a stone. Specific Gravity is why a ton of feathers takes up so much more space than a ton of lead. It is also the reason why a 6mm round cubic zirconia weighs more than a 6mm round diamond.
Hardness: Hardness is a stone's resistance to scratch. The scale for expressing the relative hardness of a mineral was created by French mineralogist Friedrich Mohs, now known as the Mohs Scale of Hardness. The scale runs from 1 through 10, one being the softest and 10 the hardest. He tested all the minerals hardness by scratching them with one another to rank them accordingly. Diamond is a 10. Diamond is the hardest substance known to man. Sapphires are a 9. Tourmalines are 7.5.
 Refractive Index: the difference between the speed of light through air and the speed of light through a gemstone. As light travels from air into a gemstone, it slows and bends. Some gemstones are "doubly refractive". In these gemstones, light travels at different speeds depending upon which direction it is traveling within the crystal structure of the mineral. The difference between the two speeds of light travel is called birefringence. A tool called a refractometer is used to measure the refractive index and birefringence of faceted gemstones. Gemologists use this information combined with observations made through a microscope to determine the identity of an unknown gemstone. It is how they can tell a light blue stone is an aquamarine and not a blue topaz, sapphire, spinel, or glass.
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