The 423-carat (85 g) blue Logan Sapphire. As crystals, massive and granular. Sapphire is a gemstone, a variety of the mineral corundum, an aluminium oxide? It is typically blue in color, but natural "fancy" sapphires also occur in yellow, purple, orange, and green colors; "parti sapphires" show two or more colors. The only color which sapphire cannot be is red - as red colored corundum is called ruby,  another corundum variety.This variety in color is due to trace amounts of elements such as iron, titanium, chromium, copper, or magnesium. Commonly, natural sapphires are cut and polished into gemstones and worn in jewelry. They also may be created synthetically in laboratories for industrial or decorative purposes in large crystal boules. Because of the remarkable hardness of sapphires 9 on the Mohs scale (the third hardest mineral, after diamond at 10 and moissanite at 9.5) sapphires are also used in some non-ornamental applications, such infrared optical components; high-durability windows; wristwatch crystals and movement bearings; and very thin electronic wafers, which are used as the insulating substrates of very special-purpose solid-state electronics (especially integrated circuits and GaN-based LEDs).
Sapphire is the birthstone for September and the gem of the 45th anniversary. A sapphire jubilee occurs after 65 years. An uncut, rough yellow sapphire found at the Spokane Sapphire Mine near Helena, Montana. Sapphire is one of the two gem-varieties of corundum, the other being ruby (defined as corundum in a shade of red). Although blue is the best-known sapphire color, they occur in other colors, including gray and black, and they can be colorless.
A pinkish orange variety of sapphire is called padparadscha. Significant sapphire deposits are found in Eastern Australia, Thailand, Sri Lanka, China (Shandong), Madagascar, East Africa, and in North America in a few locations, mostly in Montana. Sapphire and rubies are often found in the same geological setting.  Every sapphire mine produces a wide range of quality - and origin is not a guarantee of quality. For sapphire, Kashmir receives the highest premium although Burma, Sri Lanka, and Madagascar also produce large quantities of fine quality gems.
 The cost of natural sapphires varies depending on their color, clarity, size, cut, and overall quality. For gems of exceptional quality, an independent determination from a respected laboratory such as the GIA, AGL or Gueblin of origin often adds to value. Blue sapphires are evaluated based upon the purity of their primary hue. Purple, violet, and green are the most common secondary hues found in blue sapphires.  Violet and purple can contribute to the overall beauty of the color, while green is considered to be distinctly negative.
Blue sapphires with up to 15% violet or purple are generally said to be of fine quality. Gray is the normal saturation modifier or mask found in blue sapphires. Gray reduces the saturation or brightness of the hue, and therefore has a distinctly negative effect.  The color of fine blue sapphires may be described as a vivid medium dark violet to purplish blue where the primary blue hue is at least 85% and the secondary hue no more than 15%, without the least admixture of a green secondary hue or a gray mask.  The 423-carat (84.6 g) Logan sapphire in the National Museum of Natural History, in Washington, D.
Is one of the largest faceted gem-quality blue sapphires in existence. Please be sure to check ALL the item's details to avoid confusion. The item "GIA BURMA NATURAL SAPPHIRE & DIAMOND PLATINUM Ring R9508" is in sale since Thursday, May 4, 2017.
This item is in the category "Jewelry & Watches\Fine Jewelry\Fine Rings\Gemstone". The seller is "lofg" and is located in Los Angeles, California. This item can be shipped worldwide.