Generally somewhere between 15 and 25mm in one direction or other. "One glance at the deep red seeds nestled inside of a pomegranate fruit explains why the word "garnet" comes from the Latin word "granatus," meaning "grain" or "seed." This name was given to the garnet because of its close resemblance to the succulent pomegranate seed." Garnet is the birthstone for January. These are the dark seeds. Rough as in, "What did the dog say when he sat on a bucket of my garnet crystals?" "Rough, rough." January birthstone.