Q : What is the difference between a Natural, Synthetic and an Imitation gem?
The term ’Natural Gem’ refers to a mineral possessing Beauty, Rarity and Durability; having some specific chemical, optical and physical properties and has grown naturally within the earth crust. Examples: Ruby, Sapphire, Emerald, Diamond, Garnet, etc.
‘Synthetic Gem’ refers to man-made material with similar chemical, optical and physical properties to that of corresponding natural gem. Example: Synthetic Ruby having all the properties similar to the natural counterpart.
‘Imitation’ refers to a look-alike material to that of a gem it is being imitated, without possessing its chemical, optical and physical properties. It may be a natural or a man-made material. Example: Red Spinel whether natural or synthetic can be considered as an imitation for a Natural Ruby, same way a glass or any other material with similar appearance can be an imitation for ruby.
Q : How beauty of a stone is judged?
The beauty or quality of a stone is judged by the 4C’s, i.e. Colour, Clarity, Cut and Carat Weight. Colour is judged by Hue (pure spectral colour), Tone (lightness or darkness) and Saturation (intensity), under proper lighting conditions. Clarity is judged by the presence or absence of inclusions considering their size, position, colour and number. Evaluation of cut involves the shape, cutting style, proportions, symmetry and finish which affect the overall brilliance. Carat weight refers to the size of the stone, larger the size higher the price.
For coloured stones like ruby look for the purer and richer red colour with minimum of secondary purple or brown colours while in case of diamonds (especially colourless) look for the purest white without any yellow and brown tints. The colour of a stone is also affected by the lighting conditions; for e.g. a ruby appears richer under an incandescent light as compared to daylight fluorescent lamp and on the other hand a blue sapphire appears better under daylight fluorescent lamp.
Gem materials with lesser number of inclusions in general fetch a better price. Increase in the visibility of inclusions, price decreases; the affect of inclusions is more reflected in a colourless stone like diamond as compared to coloured gems. However, few stones like sagenetic (rutilated/ tourmalinated) quartz, demantoid garnet or amber are known for their classic inclusions and hence the presence of inclusions increases beauty of these stones.
In addition to the 4 c’s, optical effects or phenomenas also add to the beauty and hence additional price to the gems as in case of cat’s eye, star, aventurescence, play of colour, colour change, etc.
Q : What is the difference between Synthetic and Glass?
A synthetic is a man-made product with optical, physical and chemical properties similar to its natural counterpart, while a glass (natural or man-made) has its own properties and only has the ability to imitate any natural gem not its properties.
Q : Why a ‘Lemon Topaz’ is certified as ‘Citrine’?
A greenish yellow stone purchased by a trader as a ‘lemon topaz’ and is certified as ‘citrine’ because of the fact that the purchased stone is a citrine but wrongly called as topaz. Both are two distinct species; Quartz is pure Silica, while Topaz is Hydroxyl Fluorosilicate of Aluminium. Both the materials can be easily differentiated on the basis of Heft, Quartz is much lighter as compared to Topaz; SG of quartz is 2.65, while that of Topaz is 3.54. Topaz has a better life because of higher RI of 1.620- 1.630, while quartz is comparatively duller with RI of 1.540 – 1.550.
When viewing the stones under a 10x or a higher magnification, Quartz commonly exhibits brown or yellow colour bands in rhombohedron orientation, 2 or multiphase inclusions, liquid fingerprints, needles, crystals, etc. Topaz exhibits cleavage planes (a flat break inside or on the surface) one of the most important and conclusive differentiating feature, non-miscible liquid inclusions, iron stained cracks, etc.
The term “lemon topaz” should not be used for “citrine or lemon coloured quartz” as it is just a misnomer.