Corundum var: Sapphire on Spinel (rare combo)

Item Description

Here we have a really interesting and rarely seen association specimen from Sri Lanka featuring a sharp, well-formed, octahedral crystal of Spinel with a deep mauve hue on the surface, which plays host to a group of little, striated prisms of dark steel-blue colored Sapphire on one face. Spinel and Sapphire (Corundum) are very close in their chemistry, they're both aluminum oxides, but Spinel also contains magnesium. The two minerals are often seen together from various marble deposits, but they are NOT typically seen growing on top of one another, especially INSIDE of one another like this. My best guess is that the magnesium was depleted before the Spinel could fully finish crystallizing, and the remaining aluminum oxide formed the little Sapphire crystals in the void of the Spinel crystal. I've seen a fair number of Sapphire crystals from Ratnapura over the years, and many Spinel crystals, but I honestly feel like this is the FIRST example we've encountered that featured the two minerals TOGETHER within the same crystal. If you collect thumbnails, gem minerals or you just like interesting mineral oddities, this is something that you're not likely to find anywhere else, so don't miss out! It's incredibly difficult to put a fair market value on such a unique piece, but I could see it in the $2,000 range for the simple fact that it's remarkably rare, yet still features two well-known recognizable species.
From the collection of William ("Bill") (1927-2006) and Anne (1928-2021) Cook of Cleveland, Ohio (#9682). This husband and wife duo were actively involved in the mineral world for many decades. Bill was a PhD geologist, and Anne was a mathematician, and they both were very serious mineral collectors. Bill served for many years as adjunct curator of mineralogy at the Cleveland Museum of Natural History, and Anne was inducted into the Micromounters' Hall of Fame on October 12, 2019. Both Bill and Anne, at various times, served as president both of the Mineralogical Society of Cleveland and of the Micromineral Society of the Cleveland Museum of Natural History, and Anne was inducted into the mi The rare barium lithium beryllium phosphate Wilancookite was named in their honor in 2015.