What is an adula?

"Adula" is a term most commonly used to refer to Moonstone, a variety of feldspar that exhibits a phenomenon known as adularescence.

Here's a breakdown:

* Adularescence: This refers to the shimmering, milky blue, white, or silvery light that plays across the surface of Moonstone. This optical effect is caused by the interference of light reflecting off internal layers of the mineral.

* Moonstone: This gemstone, often used in jewelry, is a member of the feldspar mineral family. Its name comes from its adularescence, which resembles the light of the moon.

So, while "adula" itself isn't a specific mineral name, it is associated with the adularescence effect which is most commonly seen in Moonstone.