Sphalerite.

ETYM German, from blenden to blind, dazzle, deceive, from blind blind. So called either in allusion to its dazzling luster; or (Dana) because, though often resembling galena, it yields no lead. Related to Sphalerite.
1. A mineral, called also sphalerite, and by miners mock lead, false galena, and black-jack. It is a zinc sulphide, but often contains some iron. Its color is usually yellow, brown, or black, and its luster resinous.
2. A general term for some minerals, chiefly metallic sulphides which have a somewhat brilliant but nonmetallic luster.
Zinc sulfide; name of several lustrous metallic sulfides. + prikaži više

Mineral composed of zinc sulfide with a small proportion of iron, formula (Zn,Fe)S. It is the chief ore of zinc. Sphalerite is brown with a nonmetallic luster unless an appreciable amount of iron is present (up to 26% by weight). Sphalerite usually occurs in ore veins in limestones, where it is often associated with galena. It crystallizes in the cubic system but does not normally form perfect cubes. + prikaži više

An ore that is the chief source of zinc; consists largely of zinc sulfide in crystalline form; SYN. blende, sphalerite.

ETYM Latin apertura, from aperire. Related to Aperient.
1. An opening in something.
2. An opening; usually small.
3. Controls amount of light admitted.
In photography, an opening in the camera that allows light to pass through the lens to strike the film. Controlled by shutter speed and the iris diaphragm, it can be set mechanically or electronically at various diameters. + prikaži više

A device that controls the size of aperture of the lens; SYN. stop.