Spinel on Geikeilite

specimen number:
2133366

location:
Myaing Gyi Mine, Mogok, Myanmar

description:
Red crystals of spinel on a matrix of black crystallized geikelite. in good condition.

The Myaing Gyi mine, situated within the Mogok Township of the Pyin Oo Lwin District in the Mandalay Region of Myanmar, is a historic gemstone extraction site celebrated for its production of high-quality spinel, ruby, and rare accessory minerals. Geologically, the deposit is positioned within the complex Mogok Metamorphic Belt, where the regional bedrock consists primarily of high-grade, Cambrian-aged or younger marbles, calc-silicate rocks, and gneisses that were heavily altered by hot, late-stage granitic and syenitic pegmatite intrusions during the Himalayan orogeny. This intense regional metamorphism and metasomatism subjected impure limestones to high temperatures and pressures, causing the crystallization of gem minerals within the marble matrix, which are recovered via deep underground tunnels, open-cut quarries, and secondary alluvial gravel washings. While indigenous mining has occurred intermittently in the district for centuries, formalized commercial and joint-venture operations at the Myaing Gyi tract expanded significantly in the late twentieth century, particularly during the 1990s, and localized extraction continues today under strict state-regulated mining concessions.

Geikielite is a relatively rare magnesium titanium oxide mineral, and it belongs to the ilmenite group as the magnesium-dominant end-member. Geologically, it crystallizes in high-temperature environments and is typically found within magnesium-rich skarns, metamorphosed dolomitic limestones, or as an accessory mineral in ultra-mafic igneous rocks like kimberlites and carbonatites. The mineral usually forms opaque, tabular crystals or rounded pebbles that range in color from deep brownish-black to a deep, dark red when viewed through thin edges under strong transmitted light. At localities like the Mogok gem tract, geikielite frequently occurs as a heavy accessory mineral within the gem gravels, and it can also form microscopic to macroscopic crystalline inclusions directly inside gemstone hosts like spinel, providing researchers with vital geochemical data regarding the metamorphic origin of the deposits.

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