Polariscope | Global Gemology Tools

Crossed polarising filters

When the filters are crossed, little light passes in the absence of a specimen. A gemstone may modify the transmitted light depending on crystal structure and orientation.

Single and double refraction

Ideally isotropic materials have one refractive index; anisotropic crystals generally support two optical vibration modes. Real-world strain, inclusions and twinning can complicate the pattern.

Reading a response

Rotate the sample through a full revolution and note the intensity, anomalous extinction and any interference colours. Interpret the response alongside other tests, never in isolation.

Illustrated guide

Optical properties: single and double refraction

Single refraction in an isotropic gemstone — illustrated gemology guide — **Single refraction in an isotropic gemstone**

Double refraction: perpendicular optical modes

Three polariscopes for observing light — illustrated gemology guide — **Three polariscopes for observing light**

Crossed polarising filters — illustrated gemology guide — **Crossed polarising filters**

Dark and aggregate reactions — illustrated gemology guide — **Dark and aggregate reactions**

Regular and anomalous extinction — illustrated gemology guide — **Regular and anomalous extinction**

Isotropic materials — illustrated gemology guide — **Isotropic materials**

Anisotropic gems and optical extinction — illustrated gemology guide — **Anisotropic gems and optical extinction**

Strain and anomalous reactions — illustrated gemology guide — **Strain and anomalous reactions**

Aggregate reactions in gemology — illustrated gemology guide — **Aggregate reactions in gemology**

Regular extinction — illustrated gemology guide — **Regular extinction**

Viewing along the optic axis — illustrated gemology guide — **Viewing along the optic axis**

Anomalous polariscope reactions — illustrated gemology guide — **Anomalous polariscope reactions**

Anomalous reactions in garnets — illustrated gemology guide — **Anomalous reactions in garnets**

Crystals and aggregates — illustrated gemology guide — **Crystals and aggregates**

Frequently asked questions

Can a polariscope identify a gem on its own?

No, it helps determine optical character and provides evidence that should be combined with other properties.