Gemstone Glossary

Schiller

See adularescence

Scissors cut

Mostly found in emerald cut stones, shows crossed, scissor-like crown facets. Often encountered in cheap (Verneuil) synthetics.

Scratch test

To determine the Mohs hardness of minerals, hardly used in gemmology which has to work non-destructively

Seal stone

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.

Semi-translucent

Transmitting some light only at thin edges

Shapes of cut

Most popular shapes:

Single refraction

Contrary to doubly refractive materials, singly refractive minerals do not split lightrays in two upon entry

Specific gravity

Density; the weight of a substance compared to the weight of an equal volume of water at 4°C

Square

A square shaped stone, either step- or princess cut

Star effect

See asterism

Step cut

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.

Synthetic gems

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.