Surface plates covered by this specification shall be made from fine or medium grained igneous rock such as biotite granite, biotite hornblende, diabase, hypersthene gabbro, muscovite-biotite, and muscovite biotite/granite-gneirs, etc. [...] Other granite sare acceptable provided they meet the requirements of this specification [...] and are in accordance with ASTM granite definition.
From http://w3.gsa.gov/web/p/HPTP.NSF/035c614b995c0406852565d1006211b3/b7ca77480cb48a81852565c50054b29c?OpenDocument :
Granite is defined by the American Society for Testing and Materials (ASTM) as a "visibly granular, igneous rock generally ranging in color from pink to light or dark grey, and consisting mostly of quartz and feldspars, accompanied by one or more dark minerals". The definition goes on to point out that "some dark granular igneous rocks, though not properly granite, are included in the definition." Some dark colored igneous rocks which are actually basalt, gabbro, dionite, diabase and anorthosite are quarried and sold as "black granite." These stones contain little or no quartz or alkali feldspars, but, for all practical purposes, they are used interchangeably with true granites.
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Surface plates covered by this specification shall be made from fine or medium grained igneous rock such as biotite granite, biotite hornblende, diabase, hypersthene gabbro, muscovite-biotite, and muscovite biotite/granite-gneirs, etc. [...] Other granite sare acceptable provided they meet the requirements of this specification [...] and are in accordance with ASTM granite definition.
From http://w3.gsa.gov/web/p/HPTP.NSF/035c614b995c0406852565d1006211b3/b7ca77480cb48a81852565c50054b29c?OpenDocument :
Granite
is defined by the American Society for Testing and Materials (ASTM)
as a "visibly granular, igneous rock generally ranging in color
from pink to light or dark grey, and consisting mostly of quartz
and feldspars, accompanied by one or more dark minerals". The
definition goes on to point out that "some dark granular igneous
rocks, though not properly granite, are included in the
definition." Some dark colored igneous rocks which are actually
basalt, gabbro, dionite, diabase and anorthosite are quarried and
sold as "black granite." These stones contain little or no quartz
or alkali feldspars, but, for all practical purposes, they are used
interchangeably with true granites.