Which of the following is classified as an amorphous gem?

Amber is classified as an amorphous gem because it lacks a definite crystalline structure. Unlike crystalline materials, which have long-range ordered atomic arrangements, amorphous materials do not exhibit such organization; instead, their atomic arrangement is more random. Amber, being fossilized tree resin, solidifies into a gel-like substance that retains this amorphous quality.

In contrast, diamond, quartz, and sapphire are all crystalline gemstones, each having a well-defined and ordered internal structure that contributes to their unique physical properties and appearances. This distinction in structure is essential when categorizing gemstones into crystalline or amorphous types.