The Daily Croissant

"The blue brilliance of the sapphire has been treasured for thousands of years, its color thought to represent heavenly or celestial qualities. The ancient Persians believed that the earth rested on a giant sapphire and that its reflection gave the sky its blue color. Jewish tradition holds that Moses was given the Ten Commandments on tablets of sapphire, making it the most sacred of gemstones. 

Sapphire is a form of the mineral corundum, a crystalline form of aluminum oxide and one of the most durable minerals that exists; only diamonds are harder. Trace impurities of iron and titanium are responsible for the deep blue color most people associate with sapphire. The gem also occurs in a variety of blue shades. Several other colors of corundum, such as yellow, reddish-orange, and violet, are also classified as sapphire. Red corundum crystals are called rubies. When cut into a cabochon (a convex, unfaceted form), some specimens of sapphire exhibit asterism; that is, a six-rayed star can be seen in the interior of the stone. Such stones are called star sapphires."

Ruby has been the world's most valued gemstone for thousands of years. In the ancient Sanskrit language, it was called ratnaraj or "king of precious stones". Even today, rubies are considered more valuable and rare than even the top quality colorless diamonds.

These gemstones are red variations of the mineral corundum, a crystalline form of aluminum oxide and one of the most durable minerals that exists; only diamonds are harder. The rich red color arises from the substitution of a small number of aluminum atoms by chromium atoms. Pure corundum is a colorless, trigonal crystal, but it occurs in a wide variety of colors due to infiltrations of other elements. All color variations of corundum, with the exception of ruby, are called sapphires.

by Wendy Van Norden

"The photo above shows travertine covering the outside surface of the J. Paul Getty Museum in Los Angeles, California. In this close-up, you can clearly see leaf fossils, evidence of the shallow water environment in which the travertine formed. Rainwater becomes acidic when it absorbs carbon dioxide (CO2) from the air. As this rainwater seeps into the ground, it dissolves the calcite in limestone layers. If this water should make its way back to the surface, bubbling up from a spring, for example, the saturated groundwater would release the CO2 and precipitate the calcite around algal mats, bacteria and even leaves.

The travertine of the Getty Museum comes from the most famous travertine quarry in the world, the Bagni di Tivoli, which is located east of Rome, Italy. It's the same travertine used to build the Coliseum, the Trevi Fountain and the colonnade of Saint Peter's Basilica."