Gems in the display case, call it a rock-a-thon

from Kanye West (Ft. Ghostface Killah & Pusha T) – New God Flow Lyrics on Rap Genius

Meaning

Gems, also known as gemstones, are minerals that, when polished are used to make jewelry. Though most gems are minerals, few rocks also fall into the gemstone category. A rock-a-thon implies that there are many gems, further implying that he is very rich.
Ghostface must have learned a thing or two from Bill Nye as did the rest of us.

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