If you read information about mineraloids written by a variety of authors, you will discover that some authors include organic materials, such as amber and jet, in their list of mineraloids. Some mineralogists agree with such classifications, but others feel this stretches the definition of a mineraloid too far.

Amber is a fossil plant resin found in sediments and sedimentary rocks in many parts of the world. It is hard, brittle, translucent to transparent, and is often cut as a gemstone. It has the appearance of a mineral, but lacks an ordered internal structure and lacks a definite chemical composition. Furthermore, it is organic. It fails three of the five tests for being a mineral. Should it be called a “mineraloid”?

Jet is a rare type of dark black coal. It has a smooth texture that accepts a bright polish, which is why it is often cut as a gemstone. It has the outward appearance of a mineral but lacks a crystalline structure and a definite chemical composition. It is also organic. Should it be called a “mineraloid”?

A number of very tiny organisms, such as diatoms and radiolarians, produce a thin shell of amorphous silica known as a “test.” When these organisms die, their tests sink to the bottom. When the tests are the dominant material that accumulates, the sediment is known as “ooze.” If buried and lithified, the ooze can transform into rocks such as diatomite and radiolarite. If they are composed of amorphous silica, should they be called mineraloids?