Hardness Scale –
Different gemstones can be distinguished by their scratch hardness. The Viennese mineralogist Friedrich Mohs originated the term scratch hardness, which is the resistance of a mineral when scratched with a sharp object. It has set up a comparison scale using 10 minerals of different hardness levels, which ranges from 1 to 10 (1 being the lowest and 10 the hardest), which is still in use today. Gemstones scratch hardness 1 and 2 are considered soft, those from 3 to 5 semi or medium hard and those over 5 are very difficult.
Cleavage and Fracture –
The cleavage of a kind of a gemstone is the manner in which mineral can separate and split off. Gemstones may be “cleave” along specific levels where the atomic bonding is smaller. Cleavage is usually used to divide large gems crystal or to remove broken or uneven pieces. The largest crystal ever found was the “Cullinan Diamond”, which was 3,106 carats in 1908 and was cleaved in 3 large parts then cleaved again into various smaller pieces.
When dealing in the gem trade, there are 4 main units of measure used as units of density. There is the carat, gram, momme, and grain. The carat is the essential unit of weight for gemstones. It is equal to 0.2 grams or 200 milligrams. The price of one gemstone would be shown by the total numbers of carats. To mark smaller diamond, it is often represented as points. The way to look at details is that 1 carat is equal to 100 points, so a point would be equal to 0.01 or 100th of a carat. The gram is a unit of weight measure used for less precious or expensive gemstones and mainly for rough gems. Grain is the unit of weight measure for gems and is equal to 0.05 gram or of a carat. The momme is an old Japanese measure for cultured gems. One momme is equal to 8.75 carats or 3.75 gram.
Density and Specific Gravity –
Another way to measure gemstones is the measure a specific gravity. The specific gravity is the measurement of the weight of a specific item, in this case, gemstone, which is of any volume, compared to the measurement of an equal volume of water. Specific pressure is usually expressed in weight, which is the grams per cubic centimeter (g / 3 cm) or for larger gemstone kilograms per cubic centimeter (kg / 3 cm). To determine density, there are two methods that have been proven to be successful. The first way is the buoyancy method that can be done with the guidance of a Hydrostatic balance. The Hydrostatic balance uses Archimedes Principle of buoyancy which says that the buoyant energy of an object in water is equal to the weighted fluid that is relocated by the thing. The second method of determining weight is the suspension method. The suspension method states that a thing will float in the liquid of higher weight, sink in the liquid of lower weight and remain dissolved in a liquid of the same density. This is an inexpensive method that can be performed using a set of liquids where the amount of density is known.
Refraction of Light –
The amount of light that refracts in the gemstone is connected in each specific gemstone. This can be known to each specific stone. The amount of light that refract through a specific stone is called the (RI) refractive index. An (RI) refractive index can be accurately defined as the degree of the point at which light traveling in a stone is curved. The (RI) refractive index of the gemstone is between 1.4 – 3.2. In most gemstones, the elimination of pearls and gems, the ray of light is refracted when starting and is divided into two separate rays, each of which is traveling into different directions. This is called double refraction. A light refraction can be estimated by using a refractometer (link to refractometer on a website). Unfortunately testing with a common refractometer is only possible to measure the value on 1.81 and only stones with flat stones with flat face or facet are suitable. Refractometers have also identified the gemstones with a double refraction.