Aphanites (adj.aphanitic; fromAncient Greekαφανης (aphanḗs) 'invisible') areigneous rocks that are sofine-grained that their componentmineralcrystals are not visible to thenaked eye[2] (in contrast tophanerites, in which the crystals are visible to the unaided eye). Thisgeological texture results from rapid cooling involcanic orhypabyssal (shallow subsurface) environments. As a rule, the texture of these rocks is not the same as that ofvolcanic glass (e.g.,obsidian), with volcanic glass being non-crystalline (amorphous), and having a glass-like appearance.[3]
Aphanites are commonlyporphyritic, having large crystals embedded in the fine groundmass, ormatrix. The largerinclusions are calledphenocrysts. They consist essentially of very small crystals of minerals such asplagioclasefeldspar, withhornblende oraugite, and may contain alsobiotite,quartz, andorthoclase.[2]
Common rocks that can be aphanitic
editReferences
edit- ^Le Maitre, R. W., ed. (1989).A classification of igneous rocks and glossary of terms. Oxford:Blackwell Science.
- ^ab
One or more of the preceding sentences incorporates text from a publication now in thepublic domain: Chisholm, Hugh, ed. (1911). "Aphanite".Encyclopædia Britannica. Vol. 2 (11th ed.). Cambridge University Press. p. 163. - ^Bates and Jackson (1984).Dictionary of Geological Terms (3rd ed.).American Geological Institute.
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