Cryptocrystalline, Microcrystalline, Macrocrystalline

Terms Used for Crystal Size in Rocks and Minerals

Cryptocrystalline describes rocks and minerals whose crystals are so tiny that they cannot be seen with the naked eye.

Microcrystalline describes rocks and minerals composed of very small crystals that require magnification to be seen individually.

Macrocrystalline describes rocks or minerals with crystals large enough to be clearly seen.

The terms cryptocrystalline and microcrystalline are often used interchangeably, but cryptocrystalline refers more specifically to crystals so fine that they appear dense and uniform, even under magnification.

The prefix ‘crypto’ comes from the Greek word kryptós, meaning ‘hidden’.

Chalcedony is a well-known example of a cryptocrystalline material, composed of extremely fine quartz crystals.

Marble is a microcrystalline rock composed of interlocking calcite crystals that are too small to be seen clearly without magnification.

An example of macrocrystalline crystals would be the kind seen in an amethyst geode.

Article Photo

The photo at the top of our article shows crystals of the mineral olivine under powerful magnification. It was likely taken using polarised light, with the colours produced by light interference.

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Chalcedony, marble, calcite, olivine: Courtesy of Stan Celestian.