That's actually pretty diagnostic. It's not limestone. Whatever you dissolved on the surface is not really of interest - it really has to be a freshly exposed surface to be meaningful- but if it was carbonate the little drop of HCL would have filled with bubbles. I've got a strong feeling if you did crack this open you would find that the matrix is quite dark and it's volcanic.
Mind you, I'm only a professional geoscientist with 20+ years experience. I'm often wrong and haven't even held the rock in my hand, so you can believe it's whatever you want it to be
Cheers,
Andrew.