Stone, or domething equally hard, and cold.

Should have stressed, although it's hard to capture in the images, these have "layers", which end up looking like "rings" in these oval/circular cuts. Jamie, would that still be an indication of shell?

I would guess the dangly earring may be dyed seashell. The cab earrings, dyed marble, calcite, or similar. Both might be Méxican. JDA.

https://www.etsy.com/listing/657100481/vintage-operculum-and-silver-earrings

no, operculum would not be cut into ovals- their attractiveness lies in the natural colours of the dome-shapes.( i did inherit some operculum buttons, mounted with shanks, from my grandmother. i love the blue-green-)

Opercula are formed in a variety of shapes. The external outline matches the shape of the current whorl of whatever snail forms this "secondary shell" to act as a protective trap door.

Circular opercula derive from sometimes-large marine snails with round openings, and do tend to be domed and sometimes colorful—such as the cat's eye operculum from a turban snail. Viewing the flat underside (that connects to the "foot"), an operculum usually has a spiral structure, as do the primary shells. (Second and right photos here.) They do not have parallel layers, such that carving would present an "eye." But the opercula of the turban snail can be quite colorful and present an eye-like appearance (seen in the attached images).

Opercula are sometimes cut to make their shapes regular, and to fit into bezzels. Recently white opercula set in silver have been plentiful in Indian jewelry, and are called "Shiva eyes."

JDA.

these are more brown than teal colour, and grouped in pairs-

I'd guess that the green stone is dyed green onyx. It was often used in vintage mexican jewelry - this is how it looks when the color has faded.

I just found two examples on eBay of jewelry with stones that are similar to yours. They’re old Mexican pieces with faded onyx set in silver – I’ve seen similar things at local flea markets over the years.

The eBay item numbers are:

401438537401 (the better example)

401438534938

My father brought home from WWII a green operculum bracelet - his ship visited the Philippines and New Hebrides. This article shows many more examples.

https://chatsworthlady.com/2016/05/03/unusual-operculum-jewelry/