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
Merlin diamond mine mines worldwide, and a mere 5% gem-quality production at Australia's largest diamond mine, Argyle diamond mine. The high ratio of gem-quality diamonds is responsible for a relatively high value of $108 USD per carat (540 $/g). The known ore grade at Merlin is about 0.2 carats (40 mg) per tonne, although exploration continues under the mine's new owner. The largest diamond produced at the Merlin mine measured 104.73 carats (20.946 g), the largest ever found in Australia, and has been valued at over $525,000 USD . The mine and mining rights were sold by Rio Tinto Group, to Striker Resources,