Gem treatment symbols:

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ASBL    Assembled from pieces of the stated material(s) along with binders, substrates, caps, or carriers.

B    Bleached.

C    Coated.

D    Dyed.

F    Cracks & crevices filled with a fairly durable material.

H    Heated.

HP    Heated under pressure.

I    (same as S).

IMIT    Imitation – a manmade, or (usually treated) natural, material designed to resemble the stated stone but not equivalent to it chemically and physically.

L    Lasered, possibly with chemical treatment.

MM    A manmade material having no natural equivalent. (Such materials are often not marked with this symbol if the very name of the material designates A material that is generally known to the trade to be manmade).

N    Natural. This symbol is used either to emphasize that a material that the reader may imagine to be treated, is in This case untreated; or to designate that a stone that has a gemologically inaccurate colloquial name is in fact an untreated stone although not the stone the name suggests, e.g., undyed mountain “jade” .

O    Oil, resin, or wax colorless infusion, usually in the context of a transparent stone penetrated by tiny voids that would otherwise be conspicuous, e.g. emeralds.

R    Irradiated and possibly heated.

S    Stabilized (impregnated with a resin usually suitable for subsequent cutting and polishing).

SYN    Synthetic (laboratory duplicate of the natural stone, having its same chemistry and crystallography.)

U    Chemicals diffused into surface under high temperature.

W    Colorlessly waxed or oiled, usually in the context of a nontransparent stone.

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