GEOLOGY & PLANETARY SCIENCE A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z                    HOME ABOUT CATEGORIES SITE MAP COPYRIGHT ADVERTISE CONTACT entire Web this site spinel An oxide mineral, magnesium aluminum oxide (MgAl2O4), found in igneous and metamorphic rocks. It crystallizes in the cubic system, frequently forming twinned, octahedral crystals. Spinel has a glassy appearance and is black, red, blue, brown, or white in color. Ruby spinel from Sri Lanka is a valuable gemstone. Hardness 7.5–8, relative density 3.8. Related category    • GEOLOGY AND PLANETARY SCIENCE Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) BACK TO TOP