I found this 'rock' while out walking.

hard to really tell from your picture but Ill bet its either a specimen of Sphalerite with Tetrahedrite

or its a good crystal form of Bornite

These are all sulfides so you can test my guesses by knocking a teeny hunk off the rock and holding it in a lit match, you should get whitish smoke and a wiff of burning sulfur,(dont stand there breathing it) andif its bornite, itll keep burning blue. (ONLY do this smell test quickly because tetrahedrite contains antimony

We call Bornit "peacock ore" because it shows these blue and reddish colors and if those ARE bornite crystals, youve got a nice specimen.
It almost looks like its been prepped beforehand.

Sure this didnt come out of a collection?

You don't think pyrite?

all those are a kind of pyrite. "pyrite" isnt actually a single mineral, its a whole dogs breakfast of metal sulfides Thats where the colors come in

sphalerite is a zinc sulfide

bornite is a copper iron with more trace metals than "copper pyrite" (chalcopyrite.

I thought Pyrite when I first saw it, but Farmerman will have a more accurate assessment.

did not know that.

Could it be a variety of blenda called marmattite?

It really coulld be, the mins of Sphalerite group have a unit composition of A,X where A is a metal like Zn, Fe, Ni Co,Hg and X is the group anion S, Te, Se. Theyre all cubic and wed need to use a magnet and a match if weve no xray handy.
Th "blendes" are another name for the sphalerite group

thank you, the cleavege looks me familiar, but often sphalerite haven't metallic reflection if i remember correctly...

I usually go by the color ranges . and I was seeing a bit of reddish within the blue/black.
Its a nice specimen from finding on a walk in the woods.