Serpentine

Well, serpentinized harzburgite to be precise. Serpentine is an alteration of ultramafic rocks.

In this rock, you can see the minerals, or ex-minerals as the case may be:

Small (mm scale) black grains = chromite, and these are not serpentinized.

Blue-grey boxy-shaped grains with cleavage lines = orthopyroxene that has been serpentinized.

Yellow-brown-orange patches = serpentinized olivine.

Black almost glassy veins cutting everything like a mosaic = serpentine.

I never care much that these sorts of rocks are serpentinized, and generally map them as their protolith, harzburgite, that gives me more information about what's gone on. Some geologists map entire mountains as serpentine, even though its often more important to know what the rock was before it was serpentinized.