Which of the following is an example of a gem variety?

In the context of gemstones, a gem variety refers to a specific type of gemstone that is characterized by its color, composition, or other distinguishing features, often within a broader mineral family. Andradite is a variety of garnet specifically known for its unique characteristics, such as its varied colors that can include green, yellow, and black.

Ruby, amethyst, and citrine, while they are also varieties of gemstones, do not fall into the same categorical definition as andradite does within the garnet family. Ruby is a variety of corundum, amethyst is a variety of quartz, and citrine is also a specific type of quartz. Thus, andradite stands out as an example of a gem variety from within the garnet group, while the others represent varieties from different mineral categories.