What is the X in X-mas?
calcium-iron garnet, perhaps the most spectacular garnet because of its high dispersion (separation of light into colours), even greater than that of diamond, and refractive index. It is found in various colours, some of the most beautiful being yellowish (termed topazolite, because of its resemblance to topaz) and yellowish green or emerald-green (Uralian emeralds, or demantoid). Titanium may extensively replace both the iron and the silicon, as in schorlomite, or may simply produce a black colour, as in melanite. Andradite is typically found with grossular in contact-metamorphosed limestone. For details of chemistry and occurrence, see garnet.