Calaverite

In hot sulfuric acid the mineral dissolves, leaving a spongy mass of gold in a red solution of tellurium.

Later, transmission electron microscopy study suggested that the satellite reflections in calaverite were due to Au in incommensurately displacive modulation superimposed on the average C2/m structure.

Calaverite was first recognized and obtained in 1861 from the Stanislaus Mine, Carson Hill, Angels Camp, in Calaveras Co., California.

Since silver is isomorphous with gold in telluride minerals (i.e. gold atoms replace silver without automatically changing the crystal character), Genth more importantly reported the calaverite differed from sylvanite in having no distinct crystalline cleavage line, whereas sylvanite was known to have a distinct line of cleavage.

(As discussed above, both sylvanite and calaverite have since been found to be basically monoclinic, whereas the third known gold-silver telluride mineral krennerite is orthorhombic, with yet a different characteristic line of cleavage parallel to the crystal base).

Several years later, the nature of the mineral was identified, leading to a second gold rush of 1896 that included excavating the town's streets.

Calaverite ball-and-stick crystalline structure . The yellow-colored atoms represent gold.
Calaverite from the Cresson Mine , Cripple Creek, Colorado . Largest crystal is 9 mm