Well over a hundred years ago, the jewelers in America noticed that many semi-precious stones didn't sell or were not popular, diamonds included.
They invented the "birthstone" hoax and made it fashionable for people to buy jewelry containing the stones that didn't sell before. They took advantage of the occultism fad sweeping New England at that time and soon "birthstones" (connected to the birth months of the Zodiac) were all the rage.
Diamonds were also heavily marketed. The gemstone was abundantly plentiful and cheap - so the jewelers who owned the diamond mines artificially restricted the flow of diamonds from their warehouses and cut back on how many were mined. Then they embarked on a marketing campaign (DeBeers) to make diamonds the wedding ring gemstone. At first it was the "one month salary" ring, and that has increased over the years to the "two month salary" ring, costing thousands of dollars.
The exact same marketing ploys were used by the New Age store owners, who found that only certain stones sold or were popular, so they researched the mythical "properties" of the stones they could find information about, from all cultures, and the stones that weren't assigned mythical properties - they made those up. They then began to spread these fables of this stone doing this and that stone doing that, and pretty soon all kinds of people were buying worthless rock after worthless rock for their "magical qualities" and the store owners were raking in the cash.