The latest gem sale from Firestone Diamonds earned the exploration and mining company a disappointing $0.86m after it sold just 14% of its available carats.The firm was able to shift 3,395 carats for $863,037, however the remaining 20,100 carats did not reach reserve prices after sales faltered in the wake of market instability. The diamonds were consequently withdrawn from sale. Overall rough diamond prices have seen a drop of around 15 to 20% since the beginning of August. A number of enquiries into the remaining diamonds have since been made, the company said, but these will be held until the next diamond sale. The company said: "Rough diamond prices increased approximately 40% in the first half of 2011, driven by significant growth in demand from China and India. With continued growth expected in demand from these countries and insufficient new production to address the current shortfall in supply, the prospects for rough diamond prices remain positive."We expect that stability will return to the rough diamond market later in 2011 and that the shortfall in rough diamond supply will limit any further significant decreases in rough diamond prices."The share price dropped 5.59% to 21.12p at 12:28. NR