Barbra Hambly's ebon Darwath rock...

[Nik_2213]

One of the persistently unsettling features of Barbra Hambly's epic 'Darwath' tales and their tangents is that ebon-black rock.

Slabs sealing 'Dark' nests.
Plazas around 'Dark' nests.
The Keeps...

My take on it was a synthetic Basalt, made by 'MAGIC' as, by Clarkian definition, 'Beyond their current, post-Dark tech'.

Is there any natural material that could pass for such ?
Such that an OTL ghost-hunter could notice a singular paving slab of such ebon-black in a spooky, Medieval-ish under-croft.
And, being well-read, get the proverbial goose-bumps...

{ Spoiler: Not 'Magic', 'The Dark', nor a 'lid' on 'Unseelie', but a place-holder... }

Yes, yes, Obsidian, but that is brittle, with conchoidal fractures: Getting a paving slab of the stuff ??

Some granites are very, very dark and remarkably close grained, could such serve ??
What is the 'whatever' that gets carved for black biers and such ??

 

[Nik_2213]

All classic 'Black Marble' has pretty veins, though several do approach 'Hambly Black' ...

A friend suggested a potential rock-type, high-quality now rare, but plausibly local to UK find.
Ashford Black Marble
https://en.wikipedia.org/wiki/Ashford_Black_Marble#Geology
quote:
Geology
Although referred to as marble, the rock is of purely sedimentary origin. It is a dark, fine-grained, muddy Carboniferous limestone, rich in bitumen which gives it its dark grey colouration which turns a glossy black when polished and surface treated. The prime source of this rock was from Arrock Mine, and later in 1832 from nearby Rookery Plantation,[1] near Ashford-in-the-Water.
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