The polariscope

The stone is tested by rotating it 360°, between the crossed polarising filters.

The isotropic or cubic mineral stays dark and unchanged. The anisotrop or birefringent mineral produces a light and dark blinking, 4 times during one rotation of 360°. Attention a minearal which is observed in the direction of the C axis, behaves like isotopic. It is therfore necessary to observe all minerals in more than one direction. The micro cristalline mineral stays bright permanently. Internal tensions become visible. Like clouds passing over the stone during its rotation. This effect is demasking synthetic spinells of the Verneuil type. Certain diamonds and garnets may produce a similar effect.

The polariscope is used to test quantities of stones either cut or rough.
It allows you to place the tested stone in one of these 4 groups:

isotropic unirefringent cubic amorphous Analcime Cubic Zirkonia Cuprite Diamond Djevalite Fabulite Fluorite Gahnite Garnet         Almandine         Andradite         Topazolite         Demantoid         Grossular         Hessonite         Melanite         Pyrope         Rhodolite         Spessartite         Tsavorite         Uvarovite Hauyne Melanite Periklas Pollucite Sphalerite Spinel YAG Glass         Moldavite         Obsidian         Tektite

anisotrope birefringent Anatase Apophyllite Skapolite Vesuvianite Wulfenite Zircon Apatite Benitoite Beryl         Aquamarine         Bixbit         Goshenite         Heliodor         Morganite         Emerald Zinkite Calcite Dioptase Corundum         Ruby         Sapphire Phenakite Quartz         Amethyst         Ametrine         Rockcrystal         Smoky Quartz         Citrine Rhodochrosite Turmaline         Dravite         Indigolite         Rubellite Andalusite Anglesite Cerussite Chrysoberyl         Alexandrite Enstatite Hemimorphite Kornerupine Cordierite Peridot Phrenite Sinhalite Topaz Zoisite         Tanzanit Azurite Diopside Epidote Euclase Feldspar         Amazonite         Labradorite         Mikroklin         Moonstone         Orthoclase         Oligoclase         Sunstone         Sanidine Clinohumite Petalite Spodumen         Kunzite         Hiddenite Staurolite Titanite Vivianite Amblygonite Axinite Disthene, Cyanite Ulexite

micro cristallic Amber Opal         Fireopal Agate         Aventurine         Calcedony         Carneol         Chrysoprase         Moosagate

false double refraction due to internal tensions Diamond Garnet Amber Synthetic Spinel Plastics

The conoscope is an acessory to the polariscope and allows to visualise the axes of doubly refracting stones.