Barite -- BaSO4, Barium Sulfate
Specimen from: Groveland Mine, Dickinson County, Michigan
A fragment was removed from this 1.5" long x .5" wide x .5" thick and placed on plaster tablet below.
When this specimen is held at certain angles to the light there is a reflective sheen that the inexperienced prospector might consider to be merely calcite, but the weight would indicate that something other than simple calcite is being held.

Barite -- BaSO4
Specimen from: Groveland Mine, Dickinson County, Michigan
Image created with B&L SZ5 microscope @ 40 power, coupled to a ccd camera and computer.
This digital image color is very close to the physical.
No sublimate (except for a barely visible pinkish color) formed although considerable & prolonged heat (oxidizing part of flame) was applied to this 3/16" long x 1/16" thick x 1/16" wide crystal as the extensive plaster cracking indicates.
The crystal rests in a carved out depression to help keep the mineral in confined area so the blast from propane torch would not be dislodged.
Heat has changed the over all color of crystal to somewhat translucent to transparent and showing tiny dark inclusions.
Additional blowpipe and simple chemical tests can be applied to confirm or deny if barite.