Garnet - by The Silver Bear

GARNET

What colour are Garnets?

“Aha, I know the answer to that one!” you say. “They’re red!”

And you’d be right. You’d also be right if you said pink, or purple, or orange, or yellow, or brown, or black,

or green, blue or colorless. In fact, like Tourmaline, there isn’t a color Garnet can’t be found in. It always used to be said that Garnet occurs in every color except blue, which held true until the discovery of blue Garnets in Madagascar in the late 1990s.

There are many different types of Garnet, which can be divided into 6 main species, according to their chemical composition. Each species also differs slightly in specific gravity and refractive index.

Pyrope – a magnesium aluminium silicate - Mg₃Al₂(SiO₄)_3. Normally occurs in a deep blood red to almost

               black, sometimes with a brownish cast.

               R.I. 1.73 – 1.76.

               S.G. 3.65 – 3.87

Almandine – an iron aluminium silicate - Fe₃Al₂(SiO₄)_3. A deep, clear red.

                     R.I. 1-75 – 1.83

                    S.G. 3.95 – 4.30

                                                           

Spessartite – a manganese aluminium silicate - Mn₃Al₂(SiO₄)_3. Normally a yellow-orange color, although a

                      violet-red variety has been found in Colorado and Maine.

                      R.I. 1.79 – 1.83

                      S.G. 3.80 – 4.25

Grossular – a calcium aluminium silicate - Ca₃Al₂(SiO₄)_3.  Occurs in yellow, cinnamon (“Hessonite”), red,                    

                   green (“Tsavorite”) and colorless (“Leuco Garnet”)

                    R.I. 1.72 – 1.80

                    S.G. 3.40 – 3.70

            

Uvarovite – a calcium chromium silicate - Ca₃Cr₂(SiO₄)_3. One of the rarest Garnets, occurring as a bright          

                   Green. Gem quality found only in Russia and Finland.

                    R.I. 1.74 – 1.87

                    S.G. 3.40 – 3.80

Andradite – a calcium iron silicate - Ca₃Fe₂(SiO₄)_3. Varies in composition and may occur in red, brown, yellow

                   (“Topazolite”), green (“Demantoid”) or black (“Melanite”).

                    R.I. 1.86 – 1.95

                    S.G. 3.70 – 4.10

Within these species are other sub-species, or “varieties”, such as –

Rhodolite - a mix of Pyrope and Almandine. Often called the "Queen of the Garnets", Rhodolite has a distinctive violet tone. 
Malaia – a mix of Pyrope and Spessartite from the Umba Valley, bordering Tanzania and Kenya. Occurs in pinkish-orange to reddish-orange to yellowish-orange.

Merelani – A lighter green variety of Tsavorite from the same locality.

Recently, “Color change” Garnets have been discovered in Madagascar, Tanzania, Sri Lanka, Norway and the USA. These stones are Pyrope and Almandine in composition. They appear as a blue-green in natural light and red to purple under incandescent light. This means there is now an alternative to the other two natural color change gemstones, those being the rare and extraordinarily expensive Alexandrite, and a small percentage of Sapphires.

Garnet forms in the Isometric (cubic) crystal system, commonly producing well formed dodecahedral (12 sided) crystals.

With a hardness of 6.5 – 7.5 and no cleavage, it is a hardy stone and easy to work with.

While normally very clean stones, certain varieties of Garnet do contain inclusions. Amandine Garnets containing Rutile needles will form a star pattern called “asterism”. Known as Star Garnets, these are

relatively rare, occurring in quantity in only a few places such as India, Russia, Brazil and the U.S.A. Today most star Garnets come from Idaho and India. The stars are always 4-rayed, with one exception – Idaho very rarely has produced 6-rayed stars, though these are so uncommon that they occur in as few as 1 in 5,000 stones.

Orange Hessonite Garnets contain a veiling known as “treacle” which is an identifying feature of the stone, as with Demantoid, which contains quite unusual “horsetail” inclusions.

                                   

Summary of Garnet location and deposits
Pyrope: China, Madagascar, Myanmar, South Africa, Sri Lanka, Tanzania, USA.
Rhodolite: Brazil, India, Sri Lanka, Thailand, USA.
Almandine: Brazil, India, Madagascar, Sri Lanka and the United States. Smaller deposits exist in Austria and the Czech Republic. Almandine garnet star-stones are found in India and the United States (Idaho).
Spessartite: Brazil, China, Kenya, Madagascar, Myanmar, Namibia, Sri Lanka, Tanzania, USA. The best specimens come from Namibia and are known as "Mandarin Spessartite".
Grossular: Canada, Kenya, Mali, Pakistan, Russia, South Africa, Sri Lanka, Tanzania, USA.
Hessonite: Brazil, Canada, Madagascar, Sri Lanka, Tanzania, USA.
Leuco Garnet: Canada, Mexico, Tanzania.
Tsavorite: Kenya, Tanzania.
Andradite: Russia.
Demantoid: Russia, China, Korea,USA, Zaire.
Melanite: France, Germany, Italy, USA.
Topazolite: Italy, Switzerland, USA.
Uvarovite: Canada, Finland, India, Poland, Russia, USA.

Garnet is the birthstone for January. It has been used as a gemstone for thousands of years, having been found in ancient Egyptian, Roman and Greek jewelry.

I hope you found this interesting. Thanks for reading.

Augie