Question

Metallic lustre due to:
(A) high density of metals
(B) high polish on the surface of metals
(C) reflection of light by mobile electrons
(D) chemical inertness of metals

Answer 1

Hint: The term lustre means to the general appearance of a mineral surface in reflected light. Metallic and nonmetallic are the two types of lustre which are distinguished easily by the human eye after some practice. But it is difficult to describe and the difference between metallic and nonmetallic lustre cannot be quantified.

Complete step by step answer:
Metallic lustre refers to an untarnished metallic surface such as gold, silver, copper, or steel. These materials are opaque to light and none passes through even at thin edges.
Pyrite $Fe{{S}_{2}}$, chalcopyrite $CuFe{{S}_{2}}$ , and galena PbS are common minerals that have a metallic lustre.
Minerals occur in a great variety of colors but these colors do not vary from metal to metal but also within the mineral. In other words, identification of minerals with a metallic lustre is important for the observer to have a freshly broken surface for accurate determination of color. This is due to the mobile electrons present in metals which are excited and de-excited energy states from the reflection of light.
Hence, Metallic lustre due to the reflection of light by mobile electrons.
So, the correct answer is “Option C”.

Note: Nonmetallic luster is exhibited by light-colored minerals that transmit light either through thick portions or at least through their edges. The terms to distinguish nonmetallic lustre are vitreous, having the piece of broken glass and resinous, a lustre having the piece of resin.