The French colonial town of Santa Rosalia was built near the copper mines that extracted copper from the unusual sedimentary copper deposits. Boleite crystals can still be found in these deposits although they are scarce and not easy to find. But this is not the most accurate portrayal of its chemistry. Color is deep blue almost black to a lighter indigo blue. Luster is vitreous to pearly.
Crystals are usually translucent but some exceptional specimens are transparent.
The cubes are rarely over half an inch on each side. Individual twinned crystals are common and are often found loose without any host matrix. Cleavage is perfect in one direction. Fracture is uneven and brittle. Streak is light greenish-blue.