Silver,
Formula Ag, (latin=argentum)

Crystal system: Cubic (silver crystals are rare, the metal mostly occurs as massive deposits or as wiry threads).
Hardness: 2.5 to 3
Density: 10.5 gms/cm³
Colour: Silver-white, tarnishing to grey or black on exposure to the atmosphere.
Streak: Silver-white

Silver is found world-wide in small quantities. In larger quantities it occurs in veins deposited from hydrothermal solutions and is frequently associated with calcite and quartz. Silver is widely used in industry for photographic products, electrical equipment (it is an excellent conductor of electricity) and for jewellery.

The specimen in the picture came from Chihuahua, Mexico.