Sparkly rough Herkimer "diamonds" (a type of clear quartz from Herkimer, New York) are prong-set in sterling silver. Posts. Sterling silver findings.
About 4x6 to 4x7mm, 4-5mm deep (0.2" x 0.2" to 0.2" x 0.3", 0.2" deep).
Size and shape of stones varies slightly for all rough studs.