See adularescence
Mostly found in emerald cut stones, shows crossed, scissor-like crown facets. Often encountered in cheap (Verneuil) synthetics.
To determine the Mohs hardness of minerals, hardly used in gemmology which has to work non-destructively
Mostly oval or cushion shaped stone with slightly bevelled edge, used for engravings (mongrams, coats of arms etc.). Table can be flat or very slightly domed.
Transmitting some light only at thin edges
Most popular shapes:
Contrary to doubly refractive materials, singly refractive minerals do not split lightrays in two upon entry
Density; the weight of a substance compared to the weight of an equal volume of water at 4°C
A square shaped stone, either step- or princess cut
See asterism
Style of cutting rectangular or octagonal stones with parallel facets arranged like steps of a staircase. The classic octagonal emerald cut is a step cut.
Mostly have the same chemical, physical and optical properties as their natural counterparts. As an example for an exception: synthetic spinels have a slightly higher refractive index than natural spinels.