The Garnet Family

When we think of garnet, the collective imagination conjures up images of a red to purplish-red stone. This is actually the most common and widely used variety in jewelry, but there are many others!

We also speak of the garnet family because there is a very large variety which includes practically all colors.

What makes them garnets is their crystalline structure. They all have the same structure, but with different chemical compositions. Basically, it's a scaffolding that's arranged in the same way but with different components. And each type of garnet has a well-defined chemical composition.

They have in common the fact of being nesosilicates of formula X ₃ Y ₂ (SiO ₄ ) ₃

 with X and Y varying.

But in fact, it's not that simple, that's the theory. Because in reality, we almost never have a garnet with a chemical composition that exactly matches its definition. We almost only have mixtures with a greater or lesser proportion of one species.

We speak of a series because between two "ideal" compositions there is a very large possibility of mixing with specific characteristics. This is why we are still discovering new types of garnets.

The two main series are:

1 Aluminous garnets or pyralspites

This series includes the following garnets:

Almandine

Fe ₃ Al ₂ (SiO ₄ ) _3. Reddish-brown to purplish-red color (wine-red color) due to iron.

Pyrope

Mg ₃ Al ₂ (SiO ₄ ) ₃ blood red to pinkish red in color. Color due to chromium and iron

Pyrope-Almandin or Pyralmandin

A mixture of pyrope and almandine. In most cases they are red to purplish-red.

Rhodolite

Mixture of pyrope and almandine, pink in color.

Almandine, pyrope and especially pyrope-almandine are those most commonly found in jewelry, but this has been changing in recent years.

Spessartite

Mn ₃ Al ₂ (SiO ₄ ) ₃ from yellow-orange to reddish-brown, through to bright orange called Fanta or mandarin in reference to the drink or mandarin. Color due to manganese.

2 Garnets calcic or ougrandites

This series includes Grossular and Andradite garnets

Grossular

Ca ₃ Al ₂ (SiO ₄ ) _{3 .} Colorless, gray, pink, orange, brown, red, green, sometimes black.

Among these grossular we find

• Leucogarnet : colorless
• Hessonite : orange mainly due to iron and manganese.

• Tsavorite : green due to chromium and/or vanadium

Andradite

Ca ₃ Fe ₂ (SiO ₄ ) _3. Yellow, green or black color.

• Topazolite : yellow due to iron
• Demantoid : green due to Chromium and Iron
• Melanite: Black due to iron

The mixture of grossular and andradite gives grandite better known as Mali garnet which is increasingly sought after.

Another type of garnet:

Uvarovite

_{Ca3Cr2 ( SiO4} ) _3. Emerald green. Magnificent color, but the crystals are on the order of a millimeter and are therefore unusable in jewelry.