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…

Water and mercury are often classified as mineraloids. They are the only two natural inorganic substances that have a definite chemical composition and are liquids at room temperature. They are also the only two liquids that crystallize into minerals within the range of temperatures and pressures encountered at Earth’s surface. Water crystallizes into the mineral…

Most mineraloids form at the low temperatures and low pressures found at Earth’s surface and in shallow subsurface environments. Materials such as opal, psilomelane, chrysocolla, limonite, and a wide variety of supergene materials crystallize from gels or colloids in the shallow subsurface. Many of these materials will eventually transform into minerals with time, heat, or pressure.…

Tektites and moldavites are varieties of natural glass that formed from the impact of an asteroid or comet. These objects struck the Earth at hypervelocity, and the force of their impact produced a tremendous amount of heat energy. The explosion that occurred upon impact flash-melted the target rock and produced a shower of molten material over thousands to…

There are a number of familiar materials that can be classified as mineraloids. For example, opal is an amorphous hydrated silica with a chemical composition of SiO2.nH2O. The “n” in its formula indicates that the amount of water is variable. Therefore, opal is a mineraloid. Obsidian and pumice are igneous rocks that solidified so rapidly from a melt that their atoms were…

A mineraloid is a naturally occurring, inorganic solid that does not exhibit crystallinity. It may have the outward appearance of a mineral, but it does not have the “ordered atomic structure” required to meet the definition of a mineral. Some mineraloids also lack the “definite chemical composition” required to be a mineral. To be considered a…