Multiple choice Which of the following is an element? Ruby Sapphire Emerald Diamond Reveal answer Fill a bubble to check yourself D Correct answer Explanation Diamond is pure crystalline carbon (element C), making it an element. Ruby (Al2O3 with Cr), Sapphire (Al2O3 with Ti/Fe), and Emerald (Be3Al2Si6O18 with Cr) are all minerals containing multiple elements, not single elements.