What does anisotropic mean in mineralogy ?

Anisotropic : definition

Said of a material whose properties vary according to the orientation. In mineralogy for example, the speed of light in an anisotropic (or birefringent) crystal is variable and depends on its direction. This phenomenon results in the appearance of colors which allow the identification of the mineral with a polarizing microscope, we speak of polarization tint (see the chart of polarization tints below).

The majority of the physical characteristics of minerals are oriented and are not equivalent in all directions of space : cleavage, hardness, color, pyroelectricity, piezoelectricity, propagation of light, obey these rules.

In crystalline optics, anisotropic materials are non-cubic and non-amorphous minerals. The latter being qualified as isotropic minerals. Be careful however, an optically isotropic mineral is not necessarily so for other physical criteria. Thus the diamond which crystallizes in the cubic system is therefore optically isotropic, but has an anisotropic hardness which makes it possible to cut it.

The variations can be imperceptible for our senses and must be amplified by analytical devices to be usable (pleochroism with a polarizing filter for example). Some are visible to the naked eye and constitute excellent criteria for immediate determination (cleavage, dichroism, etc...).
Polarization shade and birefringence determination chart

ReCaptcha

This service is used to secure web forms of our website and required if you want to contact us. By accepting it you agree to Google's privacy policy: https://policies.google.com/privacy

Google Analytics

Google Analytics is a service used on our website that tracks, reports traffic and measures how users interact with our website content in order for us to improve it and provide better services.

Facebook

Our website allows you to like or share its content on Facebook social network. By activating and using it you agree to Facebook's privacy policy: https://www.facebook.com/policy/cookies/

YouTube

Integrated videos provided by YouTube are used on our website. By accepting to watch them you agree to Google's privacy policy: https://policies.google.com/privacy

Twitter

Integrated tweets and share services of Twitter are used on our website. By accepting and using these you agree to Twitter's privacy policy: https://help.twitter.com/en/rules-and-policies/twitter-cookies