I'd go for contrast. Your chances of getting a match are low and nothing looks worse than "just missed".

Quartzite?

I agree with @Joseph Corlett. You wouldn’t be able to match that stone with another piece unless you bought them together, at the same time. If you do a black addition, it will look like it was planned. Can we see the whole room and what your project is? I think it’s granite.

Agree with the above. It will be close to, if not completely, impossible to match with a new piece under the same name.

It’s a Juperana variant. Which wouldn’t match from slab to slab out of the same block mined at one time. Much less slabs mined miles apart and years apart.

try going for solid black color slab, with same gloss finish.

What did you end up doing?