殼 – Ke2, Qiao4 – Shell
蛋殼 – Dan4 Ke2 – Egg Shell
地殼 Di4 Qiao4 – Earth Shell — Crust
I found out recently from a cow orker that in Danish, kneecaps are “Knee Shells” (knæskallen). I tried to dazzle him with my encylopediac knowledge by replying “Oh yeah? In Chinese, fingernails are FINGER ARMOR!” He was insufficiently impressed.