Summary:

There are two major sources of rubies in Myanmar (Burma)—Mogok (Mandalay Division) and Mongshu (southern Shan State)—and several minor sources Nawarat/Pyinlon (near Namkhan, Shan State); Tanai and Nayaseik (Kachin State); Katpana (Kachin State); and Sagyin and Yatkanzin stone tracts (Madaya township) near Mandalay. Mogok and the smaller deposits are similarly hosted in white marble with considerable diversity among the rubies from each tract and strong similarities among the rubies between the tracts. Mongshu, although associated with metasediments and marbles, yields distinctly different rough and treated stones. Thus, stones from Mongshu are easily distinguished from those found at Mogok and the smaller deposits. These differences can be discerned using an optical microscope. Basic characteristics of stones from the minor sources are described, however further research is required to assess criteria for distinguishing among these sources and Mogok.

Methodology: Several hundred rubies from these source areas in Myanmar were examined for features that could be recorded photographically using a Mark 6 Gemolite with a 10X eyepiece normally at maximum magnification (~60x). Images were recorded on 35 mm Ektachrome tungsten film (ASA 160) with an "eye-piece" camera and printed electronically on a FUJIX Pictography 3000 (TDT process printer). Images are presented here at relatively low resolution.

Mogok Rubies

The classic rubies from Mogok characteristically contain short, fine, rutile needles — so-called silk. These dust-like inclusions occur either as overall cloudiness, in patches, or in distinct zonings. Generally, long slender rutile needles in reticulated patterns are more common in pinkish red rubies. B�hmite needles are restricted to twin planes and other lamella in ruby.

The other most common inclusions in Mogok rubies include colorless calcite and dolomite (sometimes yellowish)–both manifest internal twinning and/or cleave planes– prismatic apatite, feldspar, pyrrhotite, titanite, magnetite, micas, spinel, and possibly tourmaline, diopside and many other minerals. Fluid inclusions on healed fractures (healing feathers) are also typical features in Mogok rubies. Negative crystals of mixed solid and fluid are not uncommon.

Mogok rubies are known for their intense "pigeon-blood" color, enhanced by daylight fluorescence, but saturation ranges to pink. Pronounced crystallographic color zoning is rare, but subtle banding and small "swirls" of color zoning, known as treacle, are common.

Nawarat Rubies

Rubies from Pyinlon on the Nawarat stone tract occur in a crystalline marble as at Mogok. Inclusion minerals in these rubies are dominated by calcite, dolomite, and rutile with lesser numbers of apatite, feldspar, and probably pyrrhotite and spinel. Inclusion morphologies vary from euhedral to rounded and irregular. Silk tends to be less pronounced (thinner or dusty) than in Mogok rubies. Silk banding is not uncommon, but color banding, if present, is not distinct. Color swirls (treacle) has been observed. The Crown of Nawarat is 5.45 carat ruby with an exceptionally fine pigeon's blood red color, however, the majority of the rubies have medium choice color with a light purplish overtone.