Feature Gems & Gemology, Fall 1991, Vol. 27, No. 3

New Rubies from the Morogoro Area, Tanzania

The authors present the mineralogical and gemological properties of rubies found recently in the Morogoro area of Tanzania that have many features in common with rubies from Myanmar (Burma) and other comparable marble-type deposits. Specifically, microscopic investigations of these Morogoro stones revealed some internal characteristics that are also seen in Burmese rubies-such as angular growth zoning, curved growth zoning ("swirls"), negative crystals, spinel crystals, rutile needles, and clouds of minute particles in areas defined by both types of growth zones, which may also be related to color zoning. However, the Morogoro material appears to have (1) lower amounts of V and Ga than Burmese rubies, and (2) a characteristic angular growth with r, a, and r' faces. A gemological comparison of the recently produced Morogoro rubies with rubies found earlier in this area shows significant differences.