Mogok's ruby occur in a crystalline limestone (marble). Bit by bit, millions of years of weathering freed the ruby from their marble, carrying them down from the hills to the valley floors, where they have settled in the bottom of the streams and rivers. It is from these ancient river gravels (locally termed byon) that the majority of stones have been recovered in this placer.

Important sources for ruby and sapphires existed in Thailand and Cambodia. The ruby deposits occur along the Thai/Cambodia border in Chanthaburi and Trat province in Thailand, and neighboring Battambang province in Cambodia. The rubies tend to be brownish red and somewhat dark in color, while the sapphires are generally dark blue. Fine yellow sapphires can be found at Khao Ploi Waen and Bang Ka Cha, while blue sapphires are mainly found at Khao Ploi Waen, Bang Ka Cha and Bo Ram in Thailand and Pailin in Cambodia. Rubies are found in a wide area including Bo Rai, Nong Bon, Bo Waen and Tok Prom in Thailand and Pailin in Cambodia. The center for the gem trade in this area is Chanthaburi, Thailand.

In northern Vietnam the main ruby-producing sites are in Yen Bai province (the Luc Yen and Yen Bai mining districts) and the Quy Chau deposit in Nghe An province. The southern deposits of BGY sapphires (Blue-Green-Yellow sapphires) are located at Dark Nong and Binh Thuan in the Dek Lak and Lam Dong provinces respectively.

Blue sapphires from Kashmir are considered as fine quality by the auction houses to advertise their place of origin (as with Myanmar blue sapphire and ruby, Colombian emerald). The very rare and famous Kashmir blue sapphires come from India: the mining area was discovered in the late 1800s and remained productive for about ten years. The sapphires that were found are currently known as Kashmir blue sapphires, present an inimitable blue tintas “velvety”, due to the presence of minute crystalline inclusions that give the gem an extraordinary appearance.

Ruby is found in several Indian states. Facet-grade ruby has been reported from the Kangayam area of Tamil Nadu and from Karnataka. In general, the quality is not high and many stones are treated.Star rubies are fairly common.

Bowersox and Chamberlin place the Jegdalek ruby deposit in the southern part of the Sorobi district, 60 km south-east of Kabul in the Jegdalek river valley. They attribute ruby formation to the contact metasomatism of ultra-acid granites with Precambrian carbonate and magnesium rocks in the Pamir-Nuristan median mass. Ruby mineralization is irregularly developed. Gem ruby is found in situ in interstratified Proterozoic marble and gneisses intruded by granitic rocks from the Oligocene. The ruby-bearing marble is notably coarse-grained.

Corundum with a wide range of color is found in south-west Sri Lanka. Sri Lankan ruby  pink rather than crimson but stones are very bright and lively. Star rubies and blue sapphires from Sri Lanka are very beautiful color. Fine examples include the Rosser Reeves star ruby of 138.7 ct. (Smithsonian Institution) and the 392 ct. star sapphire owned by the State Gem Corporation of Sri Lanka is exceptional. Mining method is simple to reaching the illam (gem gravels, perhaps 15 m down)Virtually all Sri Lankan gems are cut and polished locally. Much blue sapphire shows the best or only blue in one part of the crystal (Ottu). Lapidaries manage to place the blue in the culet (bottom) area of the faceted stone so that the blue shows through the table.Such stones are intriguing and beautiful. Color change (blue to purple) may be seen in some unheated sapphires.

The blue sapphires found in alluvial deposits and, most unusually, in situ, near Wutu, Changle county, central Shandong Province. The sapphires show a range of color, including dark blue, blue, greenish blue and yellow. The most abundant trace elements found are iron, gallium, titanium, cobalt and vanadium. Gemological properties accord with those of other basaltic-hosted sapphires; among the mineral inclusions are uranium- and thorium-rich zircon, titanium-rich columbite, sodium feldspar, apatite, ilmenite and magnesium-iron spinel.

Highly characteristic sapphire crystals occur in a dark silica-poor lamprophyre dike consisting of biotite and pyroxene group minerals. The dike intrudes the Madison limestone and though only a few feet wide, extends for at least five miles. Yogo blue sapphires are almost recognizable from their exceptionally bright but deep colorThe crystals are not usually large. Yogo sapphires make superb melee. Lilac and purple stones can also be beautiful. A very few rubies have been found. Without doubt, Yogo sapphires are the most commercially important of all the color stones so far found in North America.

Corundum from Tanzania occurs in a wide range of color including orange, purple, mauve and yellow as well as red, green and blue. In general, the color can be said to be pastel but are particularly attractive. Ruby inclusions in a bright green chromiferous rock (Zoisite) make good carving material and have been given the vernacular name anyolite. The varieties of sapphire can be found from the Umba river valley in north-eastern Tanzania, near the Kenya border where sapphires are mined from several pits in and around a greyish green serpentine pipe. The sapphires and rubies of Umba occur in various color, often of a pastel shade which is very attractive.