Eroded calcitic base material with these black structures either embedded into or eroded out of. Exceptionally heavy for its size. No radiation being emitted. Structures under magnification or crushed color is black. Streak tends to greenish. Black structures could have been crystals and were worn down over a million years (?). Specimen measures 6 inch long, 4 inch wide and 1.5 inch thick
Collected at Halo Mine, Cardiff Township, Haliburton Co., Ontario, Canada a number of years ago.
Looks like some kind of calcite cemented breccia. I have no idea what the fragments are. 
was it collected loose on top of some ground, in a pit, trench, etc?
The bottom picture to me looks like apatite and pyroxene or amphibole grains. They look like crystals that have melted appearance and no clear terminations nor crystal shape. 
Collected several specimens loose on top of ground. Possibly removed from a cavity or some type of split in the surrounding rock structure where moving water was a factor. Or this could have happened over the say the last 50 years, being exposed to the environment after being removed as waste rock. That would account for the "melted effect". It looks very much as if the specimen were soaked in acid. The outstanding feature is the relative weight. Far to heavy for its physical size. As if the structures were metal.
Remember the calcite at Bear Lake Diggings, Quirk Lake or the Herkimer Diamond sites in N.Y. and others. Looking at it again I think the grains might be some type of pyroxene as Matt suggested. Frank
When you crush one of the 'black things', does it break into any shapes? Like cubes? Photos FOV = 5mm................Under this magnification, worn and eroded (melted appearance) crystal shapes begin to appear. Surgically (thin tipped plyers) broke several structures to look for color and shape of fragments. Color tends toward black, in thin sections color is dark greenish. Does not react to HCl 34.45%, at room temperature and crushed. I purposely picked out small,l out of the way structures so as not to mar specimen.
Dirty pyroxene? Maybe it has hematite coating? No need to worry about marring the specimen, really. Hammer some off and study the cleavage, it will give you some clues.
Test for magnetism, maybe it's magnetite.
