Final answer:
The statement about gemstones is largely correct. Gemstones are hard and colorful minerals, often with a glassy or shiny luster. Examples include rubies and emeralds, which owe their colors to trace elements within their structures.
Step-by-step explanation:
The statement is generally true; a gemstone is indeed a hard, colorful mineral that typically has a glassy or shiny luster. However, not all gemstones have a glassy luster; some can be opaque or have different types of luster.
Gemstones such as ruby and emerald are known for their rich colors and glassy luster. The color of these gem-quality crystals is attributed to the presence of trace amounts of Cr³+ impurities within the mineral's structure. Ruby, for instance, is considered an allochromatic mineral, whose color arises from these trace impurities, whereas idiochromatic minerals get their color from the essential components of their makeup.
The hardness of gemstones is also a defining characteristic, enabling them to scratch glass easily, indicating their durability and suitability for use in jewelry. For example, the mineral beryl becomes a sought-after emerald when it contains trace amounts of chromium, enhancing its green color.