I have been researching Zeus' throne, and have found several sources that say the throne was made of black marble. One source was even more specific, saying it was Egyptian black marble. I am now trying to find out how that would have been written out. The nearest I have been able to decipher was the individual corresponding words: Aigýptios mélās mármaros (Αἰγύπτιος μέλας μάρμαρος) I am not fluent in ancient Greek, Hellēnikḗ (Ἑλληνική), so I don't know if this is correct, grammatically, or if there is a more nuanced way to say it. I'e also found the term mávro marmárino (μαύρο μαρμάρινο), but I think that is modern Greek. Any help would be greatly appreciated.
There does exist a material, used since antiquity, that Renaissance Europeans identified as "Egyptian black marble". Johann Georg Keyßler wrote of one such work in Rome:
In the upper Chambers is . . . a statute of Hercules, when a Boy, tall and plump; by the Colour, indeed, it appears to be Bronze, but properly, it is a black Egyptian Marble, called by some Selcio, and by others Basaltes. This Statue was found in the Villa de Meximus on Mount Aventine, and bought by the City of Rome for a thousand Ducats.
"Basaltes" is a medieval transcription error of what the Romans originally called basanites, which they adopted from the Greek βασανίτης, which in turn originated from Egyptian bḫn. For example, Georgius Agricola wrote in De Natura Fossilium that:
Some marble is iron-gray, for example, the basaltes from Egypt that is found in Ethiopia
And Pliny's Natural History appears to describe the same material:
The Egyptians, too, have discovered in Æthiopia the stone known as "basanites;" which in colour and hardness resembles iron, whence the name that has been given to it. A larger block of it has never been known than the one forming the group which has been dedicated by the Emperor Vespasianus Augustus in the Temple of Peace.
While I don't have a Greek source, there's no doubt the Greeks would have been aware.
Since the question is inspired by a modern work of literary art, I think the balance of probability is that this is the material the original author meant.
They would probably call this Alabaster, even though strictly speaking this is not marble (but is gleams like black marble).
The name may be derived from ancient Egyptian "a-labaste", which refers to vessels of the Egyptian goddess Bast, into Greek "ἀλάβαστρος" ("alabastros") or "ἀλάβαστος" ("alabastos"). The Greek words denoted a vase of alabaster.