Terminology

Adularescence or schiller: light interacts with tiny different changes in the mineral layers to give a shimmering effect.

Biogenic: results from the activity of living organisms. Also known as organic gems but biogenic mow preferred as more accurate.

Cabachon: type of non-faceted gem fashioning. A domed & polished top surface, usually with a flat base and an oval or round outline. This brings out the best in darker stones or those translucent to opaque. can also bring out the best of colour and display optical patterns or effects (eg: opals).

Clarity: freedom from inclusions & blemishes. If something is 'clean' it has high clarity.

Coloured gemstones: the Trade refers to all gemstones that are not diamond or pearls as coloured gemstones. A collective terms to include almost all coloured gem material eg: rubies, sapphires, emerals, topaz, tourmalines, garents. Also gem varieties that may be colourless like rock crystal or colourless sapphire.

Fluorescence: UV light (short and long wave types) with waves too short for us to see. Some minerals absorb UV light and give off longer light waves that we can see, so glow.

Gems: any material with a suitable combination of attractiveness, durability & rarity, & intended for use in jewellery or adornment, esp. if cut & polished.

Gem materials: broader term. All gemstones, naturally formed as well as artifical, products in jewellery.

Gem stones: formed by nature, without human interference. Not artificial, which is partially or entirely manufactured.

Inclusions: internal festures seen in a gemstone. Can include minute crystals of other materials, cracks, fissuers, tiny gas bubbles, pockets of liquid colour variations or a combination. Inclusions can indicate how old a stone is or the environment in which it grew.

Lustre: amount of light reflected from the surface.

Ornamental gemstone: most frequent category. For use as personal adornment / jewellery. Also used in carvings, inlays, architectural elements and art.

Phenomenal stones: Where light interaction causes a variety of optical effects in gemstones. Includes cat's eye, star, play-of-colour.

Porosity: ratio of the volume of interstices of a gem material to the volume of its mass.

Pleochroism. optical phenomenon observed in certain minerals and gemstones where they display different colors when viewed from different angles or under varying light conditions.

Rough gemstone: in an unfinished state (not cut or polished) and including crstals. Often fragments of minerals that can be cut and polished to be set in jewellery.

Silk: short, fine, rutile needle-like inclusions eg: found in rubies.

Simulant: or 'imitation'. Used instead of 'fake'. Any man-made or natural material that has the same general appearance but not the same physical, chemical or optical properties.

Synthetic: same chemical composition and structure as naturally occuring material. Created in a lab.