Gemology
Table of Birth Stones:
| Month | Color | Official |
|---|---|---|
| January | Dark Red | Garnet |
| February | Purple | Amethysr |
| March | Pale Blue | Aquamarine |
| April | White | Diamond |
| May | Bright Green | Emerald |
| June | Cream | Pearl |
| July | Red | Ruby |
| August | Pale Green | Peridot |
| September | Deep Blue | Sapphire |
| October | Variegated | Opal |
| November | Yellow | Topaz |
| December | Sky-Blue | Turquoise |
Table of Gemstones differentiate to colors:
| Stone | H | S.G | R.I | SR/DR | T | Remarks |
| Aquamarine | 7.5 | 2.71 | 1.57-1.58 | Double | T | Imitated by synthetic spinel and glass |
| Chalcedony | 6.5 | 2.62 | 1.53 | Double | T | May imitate some moonstones |
| Diamond | 10 | 3.52 | 2.42 | Single | T | Natural coloured stones conduct electricity |
| Doublet (1) | 8 | 3.69 | 1.73 | Single | T | Synthetic white spinel top and base, with coloured layer |
| Doublet (2) | 7.5 | V | 1.78 | Single | T | Garnet top and glass base |
| Doublet (3) | 9 | 3.99 | 1.77 | Double | T | Natural sapphire top with synthetic sapphire base |
| Eilat stone | 5 | 2.8 | 1.50 | -------- | O | A mixture of copper minerals |
| Glass | 6 | V | V | Single | T | Bubbles and striae may be seen |
| Iolite | 7 | 2.61 | 1.53-1.54 | Double | T | Lower specific gravity and refraction than sapphire |
| Jadeite | 7 | 3.34 | 1.65 | Double | TI | A rare colour for jadeite |
| Lapis lazuli | 5.5 | 2.85 | 1.50 | Single | O | Usually shows specks of brassy pyrites |
| Moonstone | 6 | 2.55 | 1.53-1.54 | Double | T | Beat stones show bluish flash |
| Rutile | 6.5 | 4.25 | 2.62-2.90 | Double | T | Synthetic stone showing large doubling of the back facets |
| Sapphire | 9 | 3.99 | 1.76-1.77 | Double | T | The synthetic stones show curved banding |
| Spinel | 8 | 3.60 | 1.72 | Single | T | Weak reddish under the colour filter |
| Spinel (synthetic) | 8 | 3.63 | 1.73 | Single | T | Strong red under the colour filter |
| Sodalite | 5.5 | 2.30 | 1.48 | Single | O | Resembles lapis lazuli, usually no pyrites |
| Swiss Lapis | 6.5 | 2.6 | 1.54 | Double | O | Dyed jasper to imitate lapis lazuli |
| Topaz | 8 | 3.56 | 1.61-1.62 | Double | T | Denser than aquamarine which it resembles |
| Tourmaline | 7.5 | 3.08 | 1.62-164 | Double | T | Doubling of the back facets readily seen |
| Turquoise | 6 | 2.7 | 1.62 | -------- | O | Often waxed or treated |
| Zircon | 7.5 | 4.68 | 1.92-1.98 | Double | T | Stong doubling of the back facets can be seen |
| Zoisite (Tanzanite) | 6 | 3.35 | 1.69-1.70 | Double | T | Has directional colour changes of violet, blue and brown |
H=Hardness; S.G.=Specific Gravity; RI=Refractive indices; SR/SD= Single / Double Refraction T=Transparency