I find their claims for granite interesting - I haven't met a non-magnetic granite yet, and it's only some bits of granite that are harder than steel - the micas can be very soft, if it's micaceous at all. They also stain like a bastard, and the soft minerals erode out, creating a pitted surface. Of course, from the photo, what they are selling doesn't look like any granite I've ever seen - if it's just a block of shaped rock, it looks more like a slightly porphyritic andesitoid hypabyssal intrusive, and if it's a reconstituted/cemented block, then it's probably not granite at all.
At my old work, we used to mount our spectrometers on finely machined, accurately levelled granodiorite slabs. We stopped bothering some years ago, as it's not really worth the bother of shifting all the granite. When SHRIMP one gets decommissioned, the granodiorite will probably be given out to the original design team for mementos, garden rocks, or in some cases, headstones.
Hrm. The pages I'm finding imply that granite surface plates are made out of blocks, not reconstituted. The ones I've used in the past did kind of feel like there were cemented, but I put that down to the precision finish. I've only ever seen them called granite, but it wouldn't surprise me too much if they were technically some other material. This Starrett page (http://www.starrett.com/pages/860_granite_surface_plates.cfm) has some more details (from a considerably more reputable source than Grizzly).
Ok, their pink ones do look like a slightly metasomatised granite, but the black is definitely not (speaking as a geologist, there are _no_ black granites. Anyone who tells you otherwise is smoking crack or selling something.)
Looks like they are using any old rock that meets the strength and machining requirements, and calling it granite because they either follow whatever who's selling them the rock calls it, or because they think the word granite implies hardness and stability.
The Grizzly one is definitely not granite in the geological sense - it just looks wrong, and is probably an andesite. The Starret pink crystalline ones might be, but their black isnt, and looks more like some variety of basaltic intrusive rock, probably a hypabyssal dolerite/diabase (same thing, different schools of naming according to where you learnt your rocks) or fine grained gabbro.
Note: I've never met a monumental/ornamental/building purveyor of polished rock products who called their stuff what it actually _is_.
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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At my old work, we used to mount our spectrometers on finely machined, accurately levelled granodiorite slabs. We stopped bothering some years ago, as it's not really worth the bother of shifting all the granite. When SHRIMP one gets decommissioned, the granodiorite will probably be given out to the original design team for mementos, garden rocks, or in some cases, headstones.
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Looks like they are using any old rock that meets the strength and machining requirements, and calling it granite because they either follow whatever who's selling them the rock calls it, or because they think the word granite implies hardness and stability.
The Grizzly one is definitely not granite in the geological sense - it just looks wrong, and is probably an andesite. The Starret pink crystalline ones might be, but their black isnt, and looks more like some variety of basaltic intrusive rock, probably a hypabyssal dolerite/diabase (same thing, different schools of naming according to where you learnt your rocks) or fine grained gabbro.
Note: I've never met a monumental/ornamental/building purveyor of polished rock products who called their stuff what it actually _is_.
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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.
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