Piretite forms as crusts in association with an orange masuyite-like U-Pb oxide on the surface of uraninite samples (Vochten, 1996).

The secondary elements, that might be found in penroseite due to the occurrence process or the environment in which the mineral was deposited, are silver (Ag), mercury (Hg), and lead (Pb)(Gordon, 1926).

It has a metallic luster and thought to have a weak chemical bonding and that what makes it with a low hardness around 3 (Earley, 1950).

The mineral is found in the Pacajake mine in Colquechaca, 150 km (93 mi) southeast of Oruro Department, Bolivia.

It is not found in-situ, rather only in float (loose rocks) from undiscovered veins which have either been eroded away or remain hidden in the mountain above (Gordon, 1926).

It was found that it behaves like isotropic crystals in which light passes through all directions with the same speed, which is strong enough to conclude that it is isometric (Bannister, 1937).

This might give an idea of how the atoms are arranged in penroseite in the absence of a real structure determination due to the undefined composition of the mineral.