New York: Polished diamond prices fell over the past three months even as rough prices remained firm, according to information published in two indexes.

The price of 1 ct. laboratory-graded diamonds fell 6.2 percent during the second quarter, according to the RapNet Diamond Index (RAPI). The index is calculated based on listings on the online network.

The price of the specified 0.30 ct. diamonds declined 5.8 percent during the quarter; 0.50 ct. diamonds dropped 1.6 percent; and 3 ct. diamonds decreased 4.6 percent.

The declines are even steeper when examined on an annual basis. Compared with the second quarter of last year, 0.30 ct. diamond prices fell 25.8 percent, 0.50 ct. stones fell 17.5 percent, 1 ct. stones fell 15.3 percent, and 3 ct. stones fell 18.1 percent.

Meanwhile, analyst Paul Zimnisky debuted a new rough diamond price index, which says that uncut diamond prices marginally increased in the last quarter, even as they fell year-to-year.

Rough prices increased 0.22 percent in the last three months and 0.07 percent in the last month, according to the index. Prices did decline some 3.39 percent in the last six months, and 9.43 percent on an annual basis, it found.

The new index culls information from rough diamond transactions by commercial miners, and has a “minor sensitivity” to polished and diamond equity prices.