Gemstones in today’s market are commonly treated to enhance their clarity and colour. These treatments would change the appearance of an undesirable gem into that of a beautiful gem. A dealer should always disclose any treatments to the gemstone because often it’s undetectable to the unaided eye.
No treatments or untreated means the gemstone was just cut and polish straight out of the earth and did not go through any treatments. The difference in price is tremendous.