Silicon Necklace - A Sparkling Grey Colored Jewelry The Sparkling grey-colored silicon gemstone, which is also famous as silica gemstone, basically it is an idiom that is used to specify that gemstones are composed primarily of silicon oxide (SiO2). Its hardness is 7 on the Mohs scale, but it may vary depending on the specific type of silicon gemstone. Since ancient times this alluring Silicon gemstone has been used in Jewelry and decorative objects. They are properly cut and polished into various shapes, that includes cabochons, faceted gemstones, and beads. They are also used in alternative healing practices, meditation, and as decorative elements in homes and offices.