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eBay
Popularity: 
As the largest online auction site, eBay has a huge number of diamond jewelries for auction every day.
There are various diamond jewelry for auction you can find on eBay. Of course, diamond ring is the most popular item in the category, but you can also find good number of diamond earrings, diamond bracelet, and diamond necklace to bid for.
If you are only interested in loose diamonds, you can also find many of them available for auction on eBay. The website has a sub category specifically for loose diamonds, and you can find loose diamond auctions on eBay by following the link.
Gem Rock Auctions
Popularity: 
Gem Rock Auctions is a highly popular auction site for gem stones, and it has many loose diamonds for auction every day.
Examples of auctioned diamonds include 1.06 cts fancy colored diamonds, 1.02 cts fancy intense yellow natural diamond, 1 ct round brilliant cut white diamond, certified electric blue 0.48 ct diamond, and GIL certified 0.80 cts natural white diamond.
According to the website, Gem Rock Auctions has sold over 500,000 individual gemstones to the bidders.
Shop Good Will
Popularity:
Shop Good Will often has an impressive list of diamond jewelry for auction.
Common items for auctions include diamond bracelets, diamond necklaces, diamond pedants, diamond rings, and loose diamonds.
Shop Good Will is the ecommerce arm of Goodwill, a leading nonprofit organization for educational and work-related services. Goodwill has over 3,300 local stores across America.
EBTH
Popularity:
EBTH stands for Everything but The House, and it's a hugely popular online auction site with diamond jewelry for auctions.
Examples of auctioned diamond jewelry include 14K 5.41 ct emerald and diamond halo ring, Israel Gady Shemesh 18K 1.92 ctw gypsy set diamond band, platinum 2.02 ctw diamond stud earrings, Lose 0.92 ct round brilliant cut diamond with GIA online report, 14K 3.36 ctw diamond band, 14K 3.12 ctw diamond stud earrings, 14K 4.52 ctw diamond ring, and 14K 3.42 ctw diamond ring with Milgrain shoulders.
Shop LC
Popularity: 
Shop LC has a vast online auction category with many diamond jewelry to bid for every day.
Popular categories include diamond rings, diamond earrings, diamond pendants, diamond bracelets, and more.
PoliceAuctions.com
Popularity:
PoliceAuctions.com is an auction site with many buyers. The site has a good number of diamond jewelry for auction.
PoliceAuctions.com has a separate category specifically for "big diamonds". When we visited the site, we found auctioned diamond jewelry like IGL certified 14K solid yellow gold 3/4 carat marquise cut diamond solitaire ring, IGL certified 14K white gold 1/2 carat diamond earrings, IGL certified 14K solid white gold 1/5 ctw diamond solitaire ring, and IGL certified 14K solid white gold 3/4 ctw diamond solitaire ring.
JTV Auctions
Popularity:
JTV Auctions is the auction arm of JTV, one of the largest retailers in the US, with live TV programs available to 84 million households.
You can often find a diverse list of diamond jewelry to bid for at JTV auctions at any time.
Property Room
Popularity: 
Property Room is a very popular auction site with some diamond jewelry for auction.
From diamond rings to diamond earrings, you can find various diamond jewelry to bid for.
According to the website, Property Room works with 4,300 law enforcement agencies and municipalities to auction goods.
Jewelry-Auctioned.com
Popularity:
Jewelry-Auctioned.com is an online jewelry auction site with some diamond jewelry to bid for.
According to the website, Jewelry-Auctioned.com has over 190,000 members, and sold 30,000 individual pieces of jewelry for auction bidders.