Lustre (mineralogy)

Types of Lustre

• Lustre refers to radiance, gloss, or brilliance in minerals.
• Terms used to describe lustre include earthy, metallic, greasy, silky, and vitreous.
• Lustre varies on a continuum and can be combined to describe intermediate types.
• Some minerals exhibit unusual optical phenomena such as asterism and chatoyancy.
• Lustre can vary within a particular mineral species.

Adamantine Lustre

• Adamantine minerals have a superlative lustre, most notably seen in diamond.
• These minerals are transparent or translucent and have a high refractive index.
• Examples of minerals with adamantine lustre include cerussite, zircon, and cubic zirconia.
• Minerals with a lesser degree of lustre are referred to as subadamantine.
• Garnet and corundum are examples of subadamantine minerals.

Dull Lustre

• Dull or earthy minerals exhibit little to no lustre due to coarse granulations.
• These minerals scatter light in all directions, resembling a Lambertian reflector.
• Kaolinite is an example of a dull mineral.
• A distinction is sometimes made between dull and earthy minerals.
• Earthy minerals are coarser and have even less lustre.

Greasy Lustre

• Greasy minerals resemble fat or grease and often contain microscopic inclusions.
• Opal, cordierite, and jadeite are examples of minerals with a greasy lustre.
• Many greasy minerals also feel greasy to the touch.
• Greasy lustre is caused by the abundance of inclusions in the minerals.
• The lustre of greasy minerals is similar to the texture of grease.

Metallic Lustre

• Metallic minerals have the lustre of polished metal.
• These minerals work as reflective surfaces and include galena, pyrite, and magnetite.
• Metallic lustre is characterized by a high reflectivity and shine.
• Ideal surfaces of metallic minerals exhibit a mirror-like lustre.
• Metallic lustre is duller and less reflective than a true metal.

Lustre (mineralogy) Data Sources