Usually when it’s black.

As some Geologists simply state: ” there is no black Granite stone”.

And, our experience is that the Black Absolutes and the other
popular black Granites are subject to acid etching and staining
much like the calcium carbonate based stones – marble, limestone,
onyx and the like. They can lose their color, turning “charcoaly” or
Battleship Gray in the certain areas they have been affected.

Gneiss, which we don’t see as often as Granite, and is often confused
as Granite – is a veined stone and can be described as ” Granite re-melted
and re-formed ” making it pretty tough, oblivious to acids.

Regardless of the particular stone – but especially the black Granites –
which are very sexy, very popular choices of the Interior Design
and Architectural communities – we must use diamonds to wet grind
and repair any damages to the surface. These processes require
a trained and highly skilled individual in the restoration process.