Crystals

Here are some of Mother Nature's beauties that I collected and cleaned off recently down near Congress, Arizona.
Quartz (SiO2) also called silica or silicon dioxide, compound of the two most abundant elements in Earth's crust, silicon and oxygen. The mass of Earth's crust is 59 percent silica, the main constituent of more than 95 percent of the known rocks.
Here are some examples of the Quartz crystals - clusters, groups and single crystals

Limonite pseudomorphs of Pyrite crystals. Here Limonite (FeO(OH)·nH2O) has replaced the Pyrite (FeS2) while retaining the crystals form.