Rubies and Lapis Lazuli
March 22, 2011
Rubies (at right) are created when corundum (Al2O3), a very hard aluminum oxide crystal, is tainted with small amounts of chromium during crystallization. This only occurs at great pressure and temperature and must take place in the absence of silica or iron. These conditions are rare, and most natural rubies are found crystallized within a narrow band of highly metamorphosed marble in the southern Himalayas, including Afghanistan. It's believed that the unique conditions required for ruby formation occurred here as the Indo-Australian Plate drove north into the Eurasian Plate. This effectively closed the Tethys Sea and buried calcareous sediments and limestones which underwent intense metamorphic change under great temperature and pressure. Within this band of crystalline marble, as pictured here, rubies formed.
Lapis lazuli (at left) is a beautiful rock that consists of the complex deep blue mineral lazurite (Na3Ca[Al3Si3O12]S) along with various amounts of pyrite (FeS2) and calcite (CaCO3) that crystallize together, slowly, at great depth. These conditions are also quite rare and occur primarily in limestone subject to contact metamorphism from igneous intrusions. Lapis lazuli is found almost exclusively in this same Himalayan limestone belt in Afghanistan, where it's been mined for over 6,000 years. Lapis lazuli takes a brilliant polish and has been found as ornamental jewelry in tombs of the Pharaohs.
The lapis and rubies are shown here with Misbaha, a string of three groups of 33 beads which is used as an aid for prayer and meditation in Islam. Photo taken on February 22, 2011 from Bagram, Afghanistan.
Photo details: Camera Maker: Canon; Camera Model: Canon PowerShot SD940 IS; Focal Length: 5.0mm; Aperture: f/2.8; Exposure Time: 0.0025 s (1/400); ISO equiv: 80; Exposure Bias: none; Metering Mode: Matrix; White Balance: Auto; Flash Fired: No (enforced); Orientation: Normal; Color Space: sRGB.