July and the “King of Gemstones” – The Ruby Birthstone

Ruby - Identifying Origin

This article covers in great detail the various geographic regions where Ruby (Gem Corundum) is found. Since geographic origin is significant when determining value, this article may assist those wishing to understand the value of rubies.

Occurrence

 Corundum is a mineral of metamorphosed crystalline limestones and dolomites, as well as other metamorphic rock types such as gneiss and schist; also in igneous rocks such as granite and nepheline syenite. Gem corundums are often found in placer deposits. Non-gem corundum is abundant throughout the world, but gem material is more restricted in occurrence.

Burma (Myanmar): Ruby historically comes from the Mogok stone tract. The history of the mines here is long, complex, and turbulent. Gems occur in a gravel layer called byon at a depth of 20 to 100 feet and are recovered by washing and screening with broad screens and then hand-picking encouraging-looking pebbles. Corundum originates in metamorphic marbles that have largely weathered away. This is the source of the world’s finest rubies.

Thailand: The areas of major importance here are Chantabun and Battambang. The corundum deposits have only been worked in a major way in modern times. Gems are found in a sandy layer within 6 to 20 feet of the surface and are recovered by washing. Thai rubies are important on the current market because of the scarcity of Burmese gems.

Pakistan: Ruby and spinel of fine quality occur in the Hunza Valley on the Pakistan Side of the Kashmir Valley. The color is comparable to Burma ruby but the material is heavily flawed.

Sri Lanka: Sri Lanka is a source of many colors of sapphire, as well as ruby and star gems. Gems occur here in a gravel layer known as illam at a depth of up to 50 feet. The material is washed and screened, and gems are recovered by hand-picking. Sri Lanka ruby is not as good as Burma material, and the sapphires are often pale in color but can be very large.

Namibia: At Namaqualand opaque ruby is found that is suitable for cabochons.

Tanzania: Large ruby of fine color and quality is found in green, massive chromiferous zoisite. The crystals are usually opaque, and the rock as a whole is cut as a decorative material, but occasionally some small areas of this ruby are transparent enough to facet. Many colors of sapphire are found in the vicinity of Morogoro, Tanga Province, along with some ruby. The Umba River Valley is a source of fine sapphires in a wide range of colors.

Kenya: Excellent ruby is known from a small ruby mine. The ruby is pinkish but of fine color and is usually in small sizes.

Afghanistan: Ruby of fine color has come from Jagdalek, near Kabul. This is an ancient source of many of the fine stones of ancient times.

India: Mysore produces poor quality rubies but a significant amount of star ruby. Some of the stones from this area are of excellent quality but are not common.

Inclusions – What do they tell us about origin?

In general, Burmese, Thai and Australian blue sapphires contain crystals of plagioclase feldspars, orthoclase, niobite, columbite, calcite,monazite,zircon, apatite, fergusonite, and thorite.

Tanzanian sapphires contain crystals of chlorapatite, pyrite, magnetite, biotite, graphite, phlogopite,zircon, and spinel.

Brazil: (Jauru, Matto Grosso): rounded gas-filled discs that resemble bubbles.

Burma: (Mogok): Short rutile needles at 60? angles; silk consisting of hollow tubes plus crystals of rutile, spinel, calcite, mica, garnet, zircon crystals with haloes; color swirls known as treacle.

Thailand: feathers= canals and tubelike liquid inclusions; flat, brownish cavities; twin planes; crystals of niobite, almandine, apatite, pyrrhotite, plagioclase crystals in sapphires. Rutile is absent.

Pakistan (Hunza Valley): phlogopite; chlorite; monazite; spinel; rutile; magnetite; pyrite, calcite.

Tanzania (Umba River Valley): apatite; graphite; pyrrhotite.

Tanzania (Longido): pargasite, spinel, zoisite.