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_.
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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_.