Pierres précieuses

L'industrie des pierres précieuses au Sri Lanka possède une histoire longue et riche. Le Sri Lanka était affectueusement surnommé Ratna-Dweepa, ce qui signifie « Île des Gemmes ». Ce nom témoigne de ses richesses naturelles. Marco Polo écrivit que l'île possédait les plus beaux saphirs, topazes, améthystes et autres gemmes du monde.

Garnet

Garnets are a set of closely related minerals that form a group, resulting in gemstones in almost every color. Red garnets have a long history, but modern gem buyers can pick from a rich palette of garnet colors: greens, oranges, pinkish oranges, deeply saturated purplish reds, and even some blues. Red garnet is one of the most common and widespread of gems, found in metamorphic rocks (which are rocks altered by heat and pressure) on every continent. But not all garnets are as abundant as the red ones. A green garnet, tsavorite, also occurs in metamorphic rocks, but it’s rarer because it needs unusual rock chemistries and special conditions to form.

Species:
Rhodolite- violet to purplish-red;
Almandite – red, brownish-red, violetish-red or purple;Pyrope red;
Grossularite – green, yellow, brown, white, colourless, light violet, red, orangey-red; Varieties: hessonite (orange to brown), transparent, green, grossularite (tsavorite);Some show a colour change from a mauve-brown to orange-red.
Andradite – green, yellow, black. Green called demantoid (high lustre and dispersion);
Spessartite – yellow to yellow-brown, dark orangey-brown, reddish-orange, orange;
Uvarovite – emerald green, found only in tiny sizes, usually opaque.
Sources:
Rhodolite – Sri Lanka, North Carolina, Tanzania, Kenya, South Africa, Brazil.
Almandite – Sri Lanka, India, Brazil, star from Idaho – USA.
Pyrope – Czechoslovakia, South Africa, Zimbabwe – Rhodesia, Brazil, Arizona.
Grossularite – Sri Lanka, Brazil, Tanzania, Kenya, South Africa, Canada.
Andradite – demantoid: Russia, Italy; translucent yellowish or greenish-brown, Arizona.
Spessartite – Sri Lanka, Burma, Brazil, Madagascar, Tanzania, Kenya.
Uvarovite – Russia, Finland (hardly mined at all).
Toughness: Fair to good
Treatments: Almost all aquamarine is heat-treated to enhance its blue colour. Irradiation with neutron, gamma rays or with x-rays. Colour change is permanent and is an accepted practice. A morganite (pink beryl) turns deep purple blue (Maxixe type) upon ultraviolet irradiation, though the colour is not stable.
History: Since earliest times garnets have been carried as amulets against accidents in travel. Asiatic peoples and even our Southwest Indians used them as bullets, believing that their rich, glowing colour might cause more deadly wounds. The Persians have given the garnet a favoured place as a royal stone, allowing it to bear their sovereign’s image. Red garnet was once used to relieve fever, yellow garnet to cure jaundice. If the powder failed, the apothecary was accused of using a substitute.
Cuts & Uses: Usually faceted. Sometimes carved into intaglios.