With your gem scope, did you see doubling? You can look through a face up star facet and focus down to the bottom of the stone's keel. You will see a marked doubling image at the bottom of the stone. This is indicative for an OTL stone like zircon.
Under crossed polarizers (dark) you will get a birefringent blink as you turn the stone. This will eliminate singly refractive stones like glass, CZ, YAG.
Have yo taken any gemological courses?