Hi, I have noted on a fair few of the forum discussions that when people are referring to an RI of a gemstone they only state one (1) Refractive Index for a gem that is doubly refractive “Anistropic”
just wanted to say if you do not undertake a proper RI Test then you cannot add this to the list of tests you need to undertake to identify a gemstone natural or synthetic
one RI reading indicates single refractive index “isotropic” glass spinel garnet diamond etc
if you are going to do an RI test on what you believe is an “anistropic” gemstone doubly refractive then you must take the lowest and highest reading by rotating the stone 360% on the refractometer to get the actual birefringence of the stone
then you have the real RI.
Unless of course your reading is down the C axis which will show a single RI on a doubly refractive gem. which of course you need to check on another facet besides the table