Porphyritic chondrule
A porphyritic chondrule contains large crystals of olivine or pyroxene set in fine-grained material or glass.
A porphyritic chondrule is the commonest kind of chondrule, making up the large majority in most chondrites. The name comes from porphyry, an igneous rock with big crystals scattered through a finer base. In these chondrules, sizeable olivine or pyroxene crystals sit in mesostasis, the glassy or finely crystalline material that filled the gaps.
They are sorted by their main mineral: porphyritic olivine (PO), porphyritic pyroxene (PP) and porphyritic olivine-pyroxene (POP). Their textures suggest the droplets were not fully melted, so surviving seed crystals helped new crystals grow. Experiments reproduce them by heating dust to just below or around its melting point and cooling at roughly 10 to 1,000 °C per hour.
With a hand lens, porphyritic chondrules appear as round grains a millimetre or so across, with visible crystals inside. In thin section under polarised light, their crystals glow in bright interference colours, making them a favourite of meteorite photographers.
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