The Viennese mineralogist Friedrich Mohs (1773-1839) invented the scratch hardness test. He defined scratch hardness as the resistance of a mineral when scratched with a pointed testing object. Mohs chose ten minerals of different hardness for comparison and graded these minerals one to ten. Each mineral in this series scratches the previous one. Minerals of equal hardness cannot scratch each other. By comparative application of Mohs' hardness scale the hardness (according to Mohs) of every gem can be determined. Stones with scratch hardness 1 and 2 are soft, 3 to 6 medium hard, over 6 hard. Minerals of Mohs' hardness 8 to 10 are also described as "hard gems." The luster and polish of gems of hardness below 7 can be damaged by dust as this may contain small particles of quartz (Mohs hardness 7). Such stones must be carefully handled when worn or stored so that they do not come into contact with any scratching objects.

Carat: The weight used in the gem trade since antiquity. The name is derived from the seed (kuara) of the African Coraltree or from the kernel (Greek - kertion) of the Carob bean. since 1907 Europe, as well as America, has adopted the metric carat of 200mg or 0.2g. Therefore weights given for famous old diamonds often vary because local carats and not metric carats were used. The carat is subdivided into fractions (1/10ct) or decimals 1.25ct) up to two decimal places. Small diamonds are weighted in in "points" =1/100cts (=0.01cts).

The carat weight of gems is not to be confused with the carat used by the goldsmith. In the case of gold the carat is no weight measure but a designation of quality. The higher the caratage, the higher the content of gold in the piece of jewelry. The weight can be variable.

Garnet
Garnet is a group of differently colored minerals with similar chemical composition. Garnet ranges from 6.5 to 7.5 on Mohs scale of hardness. Only Rhodolite in the Garnet group has double refraction. Garnet is the January birthstone.

Tanzanite
This gemstone was first introduced by Tiffiny and Company of New York. It is mined in Tanzania, where the name is derived from. Scientists call the stone Blue Zoisite. Tanzanite is 6.5 to 7 on Mohs scale of hardness. This gemstone is also nicknamed the "Tiffany Stone." Tanzanite is getting increasingly difficult to find, and will probably double in value by the end of the year. We may not be able to get more of these once quantities are sold, due to the instability of the Tanzania government and price increases.

Spinel
Spinel occurs in all colors of the rainbow. The pigments are iron and chrome. It is rare to find large stones, and the star spinels are very rare. The name 'spinel' may mean "spark" from the Greek or "point" from the Latin. It is uncertain. 150 years ago spinel was recognized as an individual mineral. Before that time, it was known as Ruby, because it is found with Ruby. Some of the well known Rubies are really Spinels, such as the 'Timur Ruby' and the 'Black Prince's Ruby,' both of which are in the English Crown Jewels. Main deposits are found in Burma and in Sri Lanka. Spinel is 8 on Mohs scale of hardness. The chemical composition is Magnesium Aluminium Oxide.

Sapphire and Ruby
Sapphire is from the family Corundum, as is the Ruby. Sapphire is from the Greek, meaning blue. The name in antiquity and as late as the Middle Ages was understood to mean what is today described as Lapis Lazuli. Around 1800 it was discovered that Sapphire and Ruby are gem varities of corundum. In the beginning, only the blue variety was called Sapphire and the Corundums of other colors, except red, were given special names which were misleading. Two of the names were 'Oriental Peridot' and 'Oriental Topaz.' Today, all colors of Corundum, except red, are called Sapphire. Red is called Ruby. Light red, pink, or violet Corundums are called Sapphire because if they were grouped with Ruby, they would be of inferior quality. Sapphire and Ruby are 9 on Mohs scale of hardness, just under the Diamond, which is a 10. Large quantities of inclusions of rutile needles result in Cat's Eye ir Six-Rayed Star Stones. Some opinions state this asterism is not caused by rutile needles, as is the case with Rubies, but by intersecting hollow channels running in three directions. Sapphire is much more common than Ruby, because the required pigment, iron, is more common than the chrome needed for Ruby. Today the important Sapphire deposits are found in Australia, Burma, Sri Lanka, and Thailand. The most desired Sapphires used to come from Kashmir, India, but the deposit has apparently been worked out. Most stones sold today as Kashmir come from Burma. In 1894 Sapphire was discovered in Montana, but there has been no mining since the end of the 1920's. Large Sapphires are rare.

Quartz
Quartz is Silicon Dioxide. Macrocrystalline Quartz includes Amethyst, Aventurine, Rock Crystal, Citrine, Prase, Hawk's Eye, Quartz Cat's Eye, Smoky Quartz, Rose Quartz, and Tiger Eye. Microcrystalline Quartz includes Chalcedony Group - Agate, fossilized wood, Chrysoprase, Heliotrope, Jasper, Cornelian, Moss Agate, Onyx, and Sard. Amorphous Quartz includes the Opal group - Precious Opal, Fire Opal, and Common Opal. The three varities of Quartz listed have a Mohs hardness of 7.

Smoky Quartz
This material gets it's name after it's smoky color. Smoky Quartz has been falsely called Smoky Topaz. Very dark stones are called 'Morion,' the Scottish variety is called 'Cairngorm.' This material can be found worldwide.

Amethyst
This is the most highly valued stone in the Quartz group. The crystals always grow on a base. The material is found in geodes in Alluvial deposits. The important deposits are in Brazil, Uruguay, and the Malagasy Republic. The name comes from the Greek and probably means "not drunken." Amethyst was worn as an amulet against drunkeness in ancient times. It is also said to have many other supernatural powers such as: bringing luck, ensuring constancy, and protecting against magic and home sickness.

Citrine Natural Citrines are pale yellow in color and rare. Most commercial Citrines are heat-treated Amethyst or Smoky Quartz. The name Citrine is derived from its lemon-yellow color. Deposits are found in Brazil, Malagasy Republic, the U.S.A., Spain, Russia, France, and Scotland.