Rocks That Make Light?

Optical effects are when a rock/mineral refracts light in a way that makes it appear as if the rock is emitting light. To me, these are some of the coolest rocks, as some that may appear dull can change into completely new looking rocks just from the effects of light.

Adularescence

To start with, one should understand that this optical phenomena mainly takes place with silicate minerals, specifically those with what we call 'twinning'. This means their lattices have distinct symmetry allowing for the iridescence to take place. Also called the Schiller Effect, this describes the soft bluish-white light coming from stones such as moonstone, rose quartz, and types of agate. These are common with variations of a rock called Adularia (e.g. Moonstone), an orthoclases feldspar. Opal is sometimes put under this category as well as holding a category of its own: opalescence.

Aventurism

This effect gives a glittery look to the stone. The most prominent example if Sunstone. Instead of the minerals being in a twin lattice, small copper pieces reflect light when tilted at different angles giving it the glistening look.

Chatoyancy

Coming from the French word for 'cat's eye', the most known type is of course Tiger's eye. In Tiger's eye, distinct bands of color make it very sought for.

Asterism

Seen mostly in the more well known gemstones like sapphire, Asterism gives the rock a starlike design. this is created by needles of rutile, so small that they cant be seen on the surface, forming within in a manner of a star. Rutile is most commonly seen in rutilised quartz, but this isn't classified as asterism as it is in a random manner.

Labradorescence

One of my personal favorite rocks of all time in Labradorite, mainly because at first glance it appears as a dull looking 'normal' rock. But when put at the correct angle to light, it gives off

Phosphorescence/Fluorescence

Unlike all the categories mentioned above, these rocks don't use visible light. Instead Ultraviolet light is used which makes them not only interesting to look at, but easy to identify. The main difference between the two is that Phosphorescent rocks are slower in taking in light and re-emitting it. Some examples are fluorite, calcite(brown/mangan),

Iridescence

This effects is seen on the surface of the rock and is best described as having the look of light hitting a bubble. Often it is seen as a rainbow-metallic color. Examples include Bismuth, Charcolpyrite, and Haematite.

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