Cryptocrystalline chondrule
A cryptocrystalline chondrule has crystals so small they cannot be seen with an ordinary microscope.
A cryptocrystalline chondrule looks almost uniform, because its crystals are too small to resolve with a light microscope. The word means 'hidden crystals'. Under crossed polars it may show faint, patchy or wavy extinction rather than distinct grains.
These chondrules are thought to have formed from fully molten droplets that cooled very quickly, possibly faster than radial pyroxene chondrules, so that countless tiny crystals formed at once. Their compositions are usually rich in pyroxene components. They are relatively rare, making up a few per cent of chondrules.
Cryptocrystalline chondrules form the extreme end of a family of textures, ranging from porphyritic, with large crystals and incomplete melting, through barred and radial, to cryptocrystalline, with complete melting and rapid cooling. Together they show that chondrule-forming events varied widely in intensity. Their fine grain also makes them sensitive to later heating, which coarsens them in higher petrologic types.
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