Tough Enough contains the hardest minerals of corundum, spinel and diamond. Corundum includes both ruby and sapphire; these are the same mineral - aluminum oxide - whose color is determined by trace elements. Sapphire includes titanium and iron, green or yellow sapphire has iron, and pink sapphire has small traces of chromium that deepen to the full red of ruby with increased levels of chromium. Corundrum is found in silica-deficient metamorphic rock. Spinel is also an aluminum-oxide mineral though its crystal system is cubic rather than hexagonal, and red spinel has often been mistaken for ruby. Diamond is pure carbon arranged in compact and uniform cubic crystalline structure. Most diamonds come from two rare kinds of volcanic rock: lamproite and kimberlite, a form of peridotite that forms in deep pipes containing intrusions from the upper mantle. Diamonds need pressures of over 50,000 atmospheres to form, corresponding to a depth of at least 90 miles beneath the surface.

•• d i a m o n d

Diamond takes its name from the Greek adamas ("I take" or "I subdue") refering to the superior hardness; no other mineral is harder. Famous diamonds include the Koh-I-Noor diamond set in the Queen Mother's crown and on display in the Tower of London, the blue Hope diamond on display at the Smithosonian, and the Regent, which has the reputation as the most beautiful diamond, on display at the Louvre. Rough irregular shape diamonds, such as found in these designs, are called bort or boart diamonds. They are considered non-gem quality grade since they lack clarity and cleavage, and as such, they are considerably less expensive per karat than gem-grade diamonds.

•• r u b y

In Sanskrit, ruby is known as ratnaraj, "king of precious stones". Given the richness of the color and play of light within its depths, it's easy to understand why. Rubies tend to be small (< 10 carats) because chromium - the source of the deep red color - inhibits crystal growth. Most rubies come from Myanmar, Thailand, and Sri Lanka, and ruby in green zoisite comes from Tanzania.

•• s a p p h i r e

Although blue is the standard color of sapphire, sapphires can be white, yellow, orange, green or pink. Much sapphire is unevenly colored and either heat treated or cut to accenuate a more uniform color. Sapphire was widely used in jewelry for medieval kings and ecclesiastical rings, perhaps to be closer to the heavens.

•• s p i n e l

Red spinel has been mistaken for ruby in the British Imperial State Crown, no less. Spinel can be red, green, blue, brown or black. It is not as hard as corundrum (7.5-8 compared with 9) but can be just as brilliantly cut.

••  m a t e r i a l   t y p e   l i n k s

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