nailhead Dark center in a gem; see fish-eye.
native cut A poorly proportioned gemstone supposedly fashioned by primitive means; considered pejorative.
Nailhead
Round brilliant diamond with a dark centre which resembles the head of a nail; caused by a pavilion depth greater than 48 percent.
Natural ...
Nailhead, Nail Head
A diamond with a dark-looking table, usually due to the pavilion angle being too high, partially by the viewer blocking light when viewed in sub-optimal lighting.
Namibia ...
20 mm Balinese Nailhead 3/4 Hoop Earrings
Nailheads are 3mm wide
$35.99 ...
aka Calcspar, Cave Onyx, Flowstone, Iceland Spar, Lime Spar, Mexican Jade, Mexican Onyx, Nailhead Spar, Pineapple Jasper
Calcite is the one of the most common minerals on earth, constituting about 4% of the Earth's crust by weight.
As shown in the diagram below, if a round brilliant diamond is cut too deep (nailhead) or too shallow (fisheye) light leaks out of the pavilion and does not return to the observer's eye. In diamonds with too steep a crown angle ( ...
A diamond that has been cut too deep will often have a dark center called a nailhead. Diamonds that have been cut too shallow will often display a white circle around the table edge which is commonly referred to as a fisheye.
Occasionally, cut gems will show part of the seed plate or a distinctive non-natural looking inclusion called a "nailhead spicule".
 See also: Stone, Brilliant, Cut, Clarity, Diamond
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