The words quarts, quartz sound the same but have different meanings and spellings. Why do quarts, quartz sound the same even though they are completely different words?
The answer is simple: quarts, quartz are homophones of the English language.
Plural form of quart.
A very hard mineral composed of silica, SiO2, found worldwide in many different types of rocks, including sandstone and granite. Varieties of quartz include agate, chalcedony, chert, flint, opal, and rock crystal.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.