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GeneralHow to determine the quality of Chalcedony specimens

17th Apr 2021 04:08 UTCD W McClure

What are some criteria you would use to determine the quality of a chalcedony specimen?

I have a large bag of chalcedony pieces I have been sorting through to determine the keepers (hint: there are not many). The criteria I have been using is:

1) clarity

2) pleasing composition or shape

3) luster

Should I add anything else?

17th Apr 2021 05:36 UTCBob Harman

D W, Determining the quality is largely subjective.

For me, size and perfection of the whole example of big display specimens is important.

Indiana examples about 8 cm - 11 cm all variously iron stained and all nicely formed.

17th Apr 2021 05:40 UTCBob Harman

A 16 cm example, in a display case. Overall, nice shape and color.

From this locality you can't get much better.

17th Apr 2021 05:42 UTCBob Harman

Another large and well formed display case example with aesthetic iron staining

17th Apr 2021 05:48 UTCBob Harman

Finally, both halves of a 15 cm pleasing blue example with an overlying 2nd generation of druzy crystalline quartz. Not only aesthetic to my eye for displays, but a rare example. This example is kept under water to maintain its vibrant blue color.

So, for me, quality = size, color, perfection of the whole example and relative rarity.

I could add another 20 examples of Indiana botryoidal chalcedony from my collection

BOB

17th Apr 2021 18:13 UTCEd Clopton 🌟 Expert

Depends on the purpose to which the material is to be put:

Mineral specimens: aesthetic or interesting form and color, freedom from damage, suitable size for display, valid locality data

Lapidary rough: freedom from fractures and cavities, attractive color and pattern, usable size

Educational samples: how well they represent the characteristics of "ideal" chalcedony (conchoidal fracture, translucency, sharp but not dangerous edges, freedom from distracting inclusions)

17th Apr 2021 18:29 UTCNic Collado

I agree with Ed and Bob. This is an example of Saxon or Bohemian yellow and red chalcedony carved into a 35cm high jug four hundred years ago in Prague by Ottavio Miseroni, who then mounted it with gold. Attractive and rare colour, size, and a minimum of inclusions/fractures are what led him to start work on this magnificent piece.

17th Apr 2021 23:01 UTCD W McClure

Thank you, Bob, Ed, and Nic.

When I dug around in the bag of chalcedony pieces, I was looking primarily for ones which would make good mineral specimens. Unfortunately there were less then I could count on one hand, yet I'm sure someone can make cabochons from most pieces in the lot.

Pictured is the best of the specimen quality pieces.

19th Apr 2021 18:18 UTCpaul ries

My personal best

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