Spinel often occurs in association with rubies, and its host rocks are typically metamorphic rocks such as gneiss, marble, or skarn. Most gem-quality spinels are mined in Myanmar, Tajikistan, Mahenge in Tanzania, Madagascar, Kenya, Sri Lanka, Vietnam, Afghanistan, and China. Most gem-quality spinels are found in alluvial deposits, where they occur alongside minerals like rubies.

Myanmar

Myanmar is a renowned source of spinel, with spinel deposits primarily concentrated in the Mandalay region (Mogok) and the Myitkyina area of Kachin State, including two major deposits: Namya and Ywathit. Since the 20th century, Mogok in Myanmar has been one of the world’s most important spinel mining areas. Spinel often occurs as an accessory mineral in ruby deposits. Both red and pink spinels can be found in both primary and secondary deposits. Primary deposits are located within marble formations and commonly occur in association with granular diopside, mica, and blue apatite. Mogok spinels are highly sought after in the gemstone market for their rich and varied colors, hues, and high saturation levels, ranging from vivid red to reddish-orange, purple, blue, and shades of pink—both light and dark. In 2006, Man Sin discovered bright neon-red spinels, and production peaked in 2009. The Namya spinel deposit is predominantly secondary in nature; its crystals are mostly irregular or rounded. In addition to red, pink, purple, and orange hues, it also yields blue, violet, and purplish spinels, among which certain colors exhibit a neon-like brilliance. Production from this deposit is relatively unstable. The Ywathit spinel deposit is mainly an alluvial deposit, featuring pale pink, purple, orange, and various shades of red. The primary host rocks in this area include fine-grained, sugar-like white-to-gray marbles, schists, and intrusive quartz veins. Spinel is hosted within the marbles, and minerals commonly found in association with spinel include sapphire, zircon, tourmaline, garnet, quartz, phlogopite, muscovite, sillimanite, perlite mica, sphene, pyrite, and graphite. Spinels originating from primary deposits on the northern side of the Ywathit Range have undergone long-distance transport and deposition, eventually forming placer deposits in the bed of the Ywathit River.

Tajikistan

The Kuh-i-Lal spinel deposit in Tajikistan is located in the southwestern Pamir region of Badakhshan, which also encompasses the northeastern part of present-day Afghanistan. For centuries, the Kuh-i-Lal mine has been the world’s primary source of large-grain spinels. It is said that mining at this site began as early as the 7th century; many famous large-grain spinels, such as the “Black Prince’s Ruby” and the “Timur Ruby,” likely originated from this very mine. The spinels produced here are characterized by their large size and high clarity, with the dominant colors being pink and rose-pink; occasionally, large-grain red spinels are also found. Although spinels often occur in association with rubies, the Kuh-i-Lal deposit represents an exception—historically, no rubies have ever been mined from this area. The genesis of the deposit is closely linked to the widespread occurrence of ultramafic metamorphic rocks within the Ghoran Formation of the region. The Ghoran Formation consists of metamorphosed sedimentary rocks (primarily biotite gneiss and migmatites), marbles, calcareous-siliceous rocks, and secondary quartzites and amphibolites. The ultramafic rocks include “white schists” (talc-andalusite rocks), skarns rich in enstatite and forsterite, as well as skarns and schists containing sodic diopside.

Tanzania

In the 1980s, spinels associated with rubies were first discovered in the Matombo and Mahenge marbles adjacent to Morogoro Province in Tanzania. Further discoveries were made near Tunduru in 1994, and in 2000, high-quality spinels were found in white marble veins in the Ipanko area near Mahenge. Since then, spinel production has steadily increased, and Tanzania has now become the world’s second-largest producer of pink-to-red spinels. In 2007, several massive spinel crystals weighing from 6 to 54 kilograms were discovered in the Ipanko region. These enormous spinel crystals exhibit an opaque center surrounded by a transparent zone that reaches gem-quality standards. Several high-transparency, top-quality red-to-pink spinels weighing from 10 to 100 carats were cut from the transparent portions of these crystals.

Vietnam

In 1983, spinel was first discovered in An Phu, Luc Yen district, Vietnam; subsequently, several other mineral deposits were identified in the same region. Vietnam is a typical locality where spinel occurs in association with corundum. When the host rock is predominantly composed of dolomite-rich marbles, spinel becomes the primary gemstone; however, if the marble contains high calcite content, only ruby forms during metamorphism. At least two distinct genetic origins have been identified for gem-quality spinel from Vietnam: vividly red spinels and most purple spinel crystals are found in marbles formed through both metamorphic and metasomatic processes. Red spinels originating from pure marbles clearly share the same geological setting as rubies found within those marbles. Interestingly, spinels of these two different genetic origins—formed via metamorphism and metasomatism—are mined from two separate deposits: may thuong (red spinel) and congoingtroi (spinels of all colors except red). These two mining areas lie on opposite sides of the Luc Yen valley. Most of the spinels produced in Vietnam exhibit a purplish hue; the Luc Yen region is particularly renowned as a major source of pink spinel. There have been reports of red spinel being mined in Vietnam, but such specimens fall far short of the quality of truly precious red spinel. Vietnam produces abundant high-quality red-pink and blue-purple spinels. In marble veins hosting gem-quality spinel, two common mineral assemblages coexist: ① spinel-corundum-chlorite-actinolite-olivine-silicate-graphite-pyrite; ② spinel-corundum-phlogopite-feldspar-muscovite-hornblende-graphite-tourmaline-apatite-rutile-pyrite. Alluvial deposits represent the primary source of gem-quality spinel in Vietnam. Secondary deposits are mainly found within karst cavities filled with gravel or in alluvial fans and associated riverbeds of the Luc Yen valley; occasionally, spinel can also be found in rice paddies. Open-pit mining remains the dominant extraction method. In secondary deposits, minerals commonly occurring alongside spinel include pink-to-red corundum, yellow and green tourmaline, blue corundum, garnet, sillimanite, quartz, and others. The key mining sites are Truc Lau and Tan Huong. The Truc Lau deposit lies within a northwest-extending canyon that stretches for 5 km. Vietnamese spinel is celebrated for its exceptional brilliance and pinkish tones, though orange, purple, and blue spinels are also produced. Pure, flawless red spinel, however, is relatively rare in Vietnam.

Sri Lanka

Sri Lankan spinels are primarily found in alluvial deposits, often intermixed with corundum and other gemstones. Their colors span a range including gray, blue, green, and purple hues. Although Sri Lanka has also yielded some exceptionally well-colored pink, red, and cobalt-induced blue spinels, the quality of these stones varies considerably, and high-quality spinels are relatively rare. Most crystals exhibit pale, muted colors; however, starry spinels and chatoyant spinels—grayish-blue to purplish-violet in color—can occasionally be found in Sri Lanka, and these are sometimes referred to as "Ceylon spinels."