It appears as though they became popular among the wealthy during the 18th century, and much more available and affordable during the 19th century. It is estimated that currently, 78% of all engagement rings sold every year are diamond. See http://www.diamondwholesalecorporation.com/TheHistoryoftheEngagementRing.html for a more information and good story!

The word "diamond" comes from the Greek word "adamas" which means unconquerable. It is made up of pure carbon and is the hardest natural substance known to man. The earliest reference to diamonds was in the Sanskrit text Arthasastra, written around 296 BCE. Diamonds quickly became associated with divinity, being used to decorate religious icons, and were believed to bring good fortune to those who carried them. Ownership was restricted among various castes by color, with only kings being allowed to own all colors of diamond. In 2005 a team of archaeologists reported the discovery of four corundum-rich stone ceremonial burial axes originating from China's Liangzhu and Sanxingcun cultures (4000 BCE–2500 BCE) which, because of the axes' specular surfaces, the scientists believe were polished using diamond powder. The rise in popularity of diamonds as gems seems to have paralleled increasing availability through European history. Diamonds were popular gems among the moneyed aristocratic and merchant classes, and by at latest 1477 had begun to be used in wedding rings. The first known engagement ring was given by Archduke Maximilian of Austria in 1477. The wife to be, Mary, wore it on the third finger of her left hand, now known as the ring finger. This was done so that the ring touched a vein believed to go directly to the heart. In 1866, massive diamond deposits were discovered in South Africa and a major deposit was found in Siberia in 1954. In 1869, a shepherd boy discovered an 83.4 carat rough diamond in South Africa signaling the beginning of the great diamond rush. Popularity continued to rise as new cuts were developed that enhanced the diamond's aesthetic appeal, and has largely continued unabated to this day; diamonds have proven popular with all classes in society as their cost has become within reach.

According to some newly discovered cave drawings, they became popular shortly after Eve took a bite out of the apple.

When people found out how pretty they were. Thats what I think!

Only married people and rich people where them, so you must only live around rich and/or married people because I have never known diamond rings to be popular.