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Gemtype Color Shape Weight Size Clarity Price Origin
You Selected (92): Octagon Shape 12x10 mm Gems Clear All
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5.2ct Octagon Facet Bi-Color Ametrine Gem (ID: 441840)
5.19 ct Ametrine
11.7 x 10.1 mm
$ 25.95
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4.9ct Octagon Step Cut Green Agate Gem (ID: 478197)
4.92 ct Agate
11.9 x 10.1 mm
$ 9.84
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5.3ct Octagon Step Cut Green Agate Gem (ID: 478260)
5.32 ct Agate
12.2 x 10 mm
$ 10.64
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5.6ct Octagon Step Cut Green Agate Gem (ID: 468734)
5.57 ct Agate
12.3 x 10.2 mm
$ 11.14
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5.8ct Octagon Step Cut Green Agate Gem (ID: 468689)
5.83 ct Agate
12.1 x 10 mm
$ 11.66
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4.2ct Octagon Step Cut Green Agate Gem (ID: 478253)
4.23 ct Agate
12.1 x 10 mm
$ 8.46
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6ct Octagon Step Cut Green Agate Gem (ID: 468682)
6.04 ct Agate
12.2 x 10.1 mm
$ 12.08
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5.8ct Octagon Step Cut Green Agate Gem (ID: 478262)
5.80 ct Agate
12.2 x 10.3 mm
$ 11.60
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5.4ct Octagon Step Cut Green Agate Gem (ID: 477913)
5.36 ct Agate
12.2 x 10.2 mm
$ 10.72
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5.5ct Octagon Step Cut Green Agate Gem (ID: 478259)
5.54 ct Agate
12 x 10.1 mm
$ 11.08
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4.8ct Octagon Step Cut Yellow Golden Citrine Gem (ID: 460622)
4.84 ct Citrine
12 x 9.7 mm
$ 33.88
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5.4ct Octagon Step Cut Yellow Golden Citrine Gem (ID: 460615)
5.36 ct Citrine
12.1 x 10.2 mm
$ 37.52
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5.2ct Octagon Step Cut Yellow Golden Citrine Gem (ID: 460783)
5.18 ct Citrine
12.1 x 9.9 mm
$ 36.26
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5.6ct Octagon Step Cut Green Agate Gem (ID: 478081)
5.63 ct Agate
11.8 x 9.9 mm
$ 11.26
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6ct Octagon Step Cut Yellow Golden Citrine Gem (ID: 460621)
6.04 ct Citrine
12 x 10.1 mm
$ 42.28
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5.5ct Octagon Step Cut Green Agate Gem (ID: 478177)
5.46 ct Agate
12.1 x 9.8 mm
$ 10.92
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5.1ct Octagon Step Cut Yellow Golden Citrine Gem (ID: 460719)
5.09 ct Citrine
11.9 x 9.9 mm
$ 35.63
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5.3ct Octagon Step Cut Green Agate Gem (ID: 477951)
5.34 ct Agate
12.2 x 10.1 mm
$ 10.68
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6.2ct Octagon Step Cut Green Agate Gem (ID: 478340)
6.23 ct Agate
12.1 x 10.2 mm
$ 12.46
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6ct Octagon Step Cut Green Agate Gem (ID: 477941)
6.01 ct Agate
12.2 x 10.3 mm
$ 12.02
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4.6ct Octagon Step Cut Yellow Golden Citrine Gem (ID: 465516)
4.57 ct Citrine
12 x 10 mm
$ 27.97
Item in Stock
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Octagon Shape 12x10 mm Gems
Some people by gems by color or price, but for many, it is best to buy gems by shape and size - especially if you're in need of a gem to replace a previous item that was lost or damaged. Calibrated Octagon shape / Emerald-Cut, faceted and cabochon gems available now in 12 x 10 mm size range. Shop a wide range of calibrated gemstones by size online at wholesale from GemSelect.

As a general guideline, when it comes to 'calibrated' gems, they are not usually expected to be cut to exact measurements. For calibrated gemstones weighing under one carat, most jewelry settings will accommodate a gem which is within 0.2 mm of the calibrated size in order to fit a standard setting. For gemstones that weigh over one carat, a larger variance is acceptable, often round shape settings will allow 0.3 mm or slightly higher even. This small variance can usually be accommodated for most standard style settings. Round-cut gemstones should also have a greater variance in acceptable size when it comes to calibration; in fact it is usually possible to mount a round stone of any size in the closest standard setting.

Certified Customer Reviews
Overall Rating -> 10 star ratings
Colors and qualities of gems are very well represented online. Easy to use website. Great selections!
Posted By in November, 2018
Source: Bizrate
Overall Rating -> 10 star ratings
This was my second purchase from GemSelect and definitely won’t be my last! They have a very wide variety of gems and you can always find what you are looking for with ease and the prices are very good.
Posted By Jill in November, 2018
Source: Bizrate
Overall Rating -> 10 star ratings
Loved the wide selection of product
Posted By Miki in November, 2018
Source: Bizrate
Overall Rating -> 10 star ratings
finally bought the last rock to complete my ring idea; needed another white one after giving the big diamond to my daughter. a diamond that size is out of my retired-school-teacher budget, so i bought a white zircon. went back to the same place that i got my loose sapphire-- great selection, good prices, good delivery!
Posted By Ptcmom in November, 2018
Source: Bizrate
Overall Rating -> 10 star ratings
I'm always real pleased with this website, I don't think there is much you could do to make it any better. I wish the shipping charges were lower, but it is understandable.
Posted By Spinch13 in November, 2018
Source: Bizrate
Overall Rating -> 10 star ratings
This is a site that sources valuable and genuine stones forms around the world, with and honest and descriptive sections, as well as specs, and the option to have the gemstone collection one might purchased—certified! Price ranges vary, but are always affordable and always worth it, whether it’s a gift, or for a personal business.
Posted By Bradley in November, 2018
Source: Bizrate
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Size and Weight

Gems are always measured in Millimeter (mm)

Dimensions are given as;
length x width x depth,
except for round stones which are;
diameter x depth

Select gems by size, not by weight!
Gem varieties vary in density, so carat weight is not a good indication of size

Note: 1ct = 0.2g

Size Comparison Chart