Cryptocrystalline and Microcrystalline
Crypto Micro and Macro Crystalline
Cryptocrystalline and microcrystalline are terms used to describe the surface of a rock or mineral made up of crystals too small to be seen with the naked eye. The word cryptocrystalline should be used when the crystals are so small they're even difficult to see under high magnification. The prefix crypto comes from the Latin word meaning hidden or secret. Crystalline describes a naturally occurring solid that's made up of crystals.
The word microcrystalline refers to crystals which are microscopic hence can be seen often with minimal magnification.
Although not accurate, cryptocrystalline and microcrystalline are often used interchangeably when describing any rock or mineral whose crystals cannot be seen with the naked eye.
Microcrystalline should not be confused with macrocrystalline which describes crystals which are large enough to be seen with the naked eye. An amethyst geode is an example of crystals which are macrocrystalline.