The main types of gemstones found in Sri Lanka belongs to five major categories, which are; corundum, chrysoberyl, spinel, garnet and tourmaline. Ceylon Sapphire being precious stones has many variety in itself differing predominantly distinguished by its colour, density, composition, translucent, purity and cut. Sri Lanka has been satisfying different kings, nationals and elites from different part of the world for more than 2500 years and still being the leader in producing Blue sapphires and Padparadscha.
Ceylon Sapphires
In Sri Lanka Sapphires occurs in all colours and each color has its own quality disparities. Sapphires is a name generally give to the blue variety, yet it occurs in other fancy colour of Pink, Purple, Violet, Lavender, Green, Yellow, Pinkish orange (Padparadscha) the most beatutiful stone in the colored stone having highest price per carat, Red colored corundum often known as Ruby.
Sapphires or corundum is the second hardest naturally occurring mineral next to diamond. It has hardness of 9 in (1 to 10 mohs) scale. Mohs scale is used to indicate the relative hardness of minerals 1 being the lowest for Talc, 9 for sapphire and 10 for diamond. Higher the hardness, higher the scratch resistant the stone is.
| Mohs hardness | Mineral | Chemical formula | Absolute hardness[2] |
|---|---|---|---|
| 1 | Talc | Mg 3 Si4 O 10(OH)2 | 1 |
| 2 | Gypsum | CaSO4 •2H 2 O | 3 |
| 3 | Calcite | CaCO 3 | 9 |
| 4 | Fluorite | CaF 2 | 21 |
| 5 | Apatite | Ca 5 (PO 4 )3 (OH–,Cl–,F–) | 48 |
| 6 | Feldspar | KAlSi 3 O 8 | 72 |
| 7 | Quartz | SiO 2 | 100 |
| 8 | Topaz | Al 2 SiO 4 (OH–,F–) 2 | 200 |
| 9 | Corundum | Al 2 O 3 | 400 |
| 10 | Diamond | C | 1600 |
Sapphires have a specific gravity of 4. The specific gravity is the way of expressing the relative density of the stone. It is indicated how much it weighs compared to same volume of water. The specific gravity of sapphires is higher than that of diamond. Diamond has a specific gravity of 3.52 whereas sapphires is measured at 4. It is an important measuring tool for the buyers and gemologist as 1 ct of higher specific gravity stone will be smaller compared with 1 ct lower gravity gem stones.
Cleavage is the propensity of the crystals to split or dissect cleanly along distinct planes.In crystals it is easier to split the crystal in some direction than the other. For instance crystal of sodium chloride cleavage can only be achieved along the planes parallel to the cube face. Any attempt to spilt crystal along any other illogical way will shatter it.
Some gemstones does not have cleavage at all those includes quartz and among precious gems Sapphires and Rubies are said to have no cleavage. However there are occasions some sapphires appears with cleavages.
Cleavage of sapphires are weak or notably having no cleavage at all making them easy to cut in different direction. Cleavage is a critical aspect jewelers and gem cutters cannot avoid to consider. In a gemstone with perfect cleavage must be cut transverse to the cleavage of planes to avoid breakages.
Meticulous work is required when jewelers soldering the gems with cleavages. A small negligence of detail can break the stone across the cleavage due to heat generated during soldering them to jewels.
Sri Lanka is also known as the "Sapphire Capital" as it to produce some of the largest sapphires discovered in the world
This is a perfect example how a stone should not be cut. Here the Cleavage is exposed and high probability cleavage can dissect the stone when dealt with an impact.
Follow the links below to learn more about the most popular sapphire types:
| Chemical Composition | Al2O3 Aluminum Oxide |
|---|---|
| Crystalline properties | |
| -System | Trigonal System |
| -Forms | Bipyramids, Pros,s and asal Pinaoid. |
| -Habit | Bipyramidal (Barrel) for sapphires & Short Prismatic for Rubies |
| -External Features | Strong Horizontal Striations on Pyramids face. Triangular Lines on Pinacoid faces |
| Cleavage | Weak Cleavages, but parting is common |
| Hardness | 9 |
| Specific Gravity | 4 |
| Colours | Blue, Red, Pink, Purple, lavender, Violet, Green, Yellow, Golden, Orange, Pinkish Orange (padparadscha) and near Colourless. |
| Pleochroism | Strongly Dichroic for strong Colours |
| Luster | Very Bright Vitreous |
| Refractive Index | 1.762 to 1.770 |
| Birefringence | 0.008 |
| Optical Character | Uniaxial - ve |
| Dispersion | Low |
