Permafrost by permafrost. Of this area slightly more than half is underlain by continuous permafrost, around 20 percent by discontinuous permafrost, and a little less than 30 percent by sporadic permafrost. Most of this area is found in Siberia, northern Canada, Alaska and Greenland. Beneath the active layer annual temperature swings of permafrost become smaller with depth. The deepest depth of permafrost occurs where geothermal heat maintains a temperature above freezing. Above that bottom limit there may be permafrost, whose temperature doesn't change annually—"isothermal permafrost". Permafrost typically forms in any climate where the mean annual air temperature is less than the
Kelsey Lake Diamond Mine America. The gem was cut and polished by legendary New York diamond cutter Bill Goldberg which yielded a faceted stone that sold for $87,500. In July 1997, the company found two gem-quality stones weighing in at 16.3 carats and 28.2 carats. The 28.2 carat diamond was cut into a 16.86-carat stone, one of the largest finished stones ever produced in North America. The cut diamond is bigger than the gemstone produced from the "Uncle Sam" diamond, which was cut into a 12.42-carat stone. Kelsey Lake Diamond Mine Kelsey Lake Diamond Mine is a defunct diamond mine in Colorado, USA. It