A rarely encountered Lutetium Yttrium Oxyorthosilicate gemstone.

Lutetium Yttrium Oxyorthosilicate, also known as LYSO, is a complex lab-created compound with chemical formula Lu_2(1-x)Y_2xSiO_5.
Grown using the Czochralski pulling method, it is mostly used in industry as a scintillator crystal for gamma radiation detection.

As a gem material it displays good lustre and moderate dispersion, with an R.I. of 1.82.a hardness of 5.8 on Moh's scale, although its brittle nature makes it difficult to facet.

It's most notable property though is it's reaction to UV illumination, displaying a very bright chalky blue fluorescence when exposed to long-wave UV (image 4) and a slightly more intense reaction to short-wave light (images 5 and 6).

weight:  12.05 carats
shape:   Oval cut, checkerboard crown facets
dimensions:   14.37 x 11.16 x 9.41 mm
treatment:  None