Mesostasis
Mesostasis is the glassy or finely crystalline material filling the spaces between larger crystals in a chondrule or igneous rock.
Mesostasis is the material that fills the gaps between the main crystals in a chondrule or quickly cooled igneous rock. It represents the last liquid, which either froze to glass or crystallised into tiny grains.
In chondrules, the mesostasis is usually richer in silicon, aluminium, calcium and sodium than the olivine and pyroxene crystals around it, because those elements were left behind in the melt. In unequilibrated chondrites, mesostasis is often clear glass. As the parent body warmed, it slowly crystallised, producing fine feldspar.
Mesostasis is chemically reactive. In carbonaceous chondrites, water altered it to clays early on, so changes in the mesostasis are among the most sensitive signs of aqueous alteration. In ordinary chondrites, the degree to which mesostasis has crystallised is one of the features used to tell petrologic type 3 subtypes apart. It can also trap sodium and other volatile elements lost from chondrules during heating.
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