Pink Peruvian opal pillow tiles and black onyx. This hand knotted necklace is 27 inches long, finished with a lobster-claw clasp.
The beads are from Bead Inspirations (https://www.beadinspirations.com), my local bead purveyor.
Both Opal and Onyx are part of the silicon-dioxide mineral family (SIO2 + (H2O)x).
Depending on the amount of water included in the matrix, the crystallographic structure, and the additional ions incorporated in the crystal, opal ranges from opaque to almost transparent. It can be colored white, black, green, pink, brown, or combinations of all of these. Opal can also exhibit ‘fire’ in addition to color (opalescence), if the crystal structure allows for internal reflection and refraction of light.
Onyx, similarly can be black, green, yellow, red, orange, black & white striped (called sardonyx, historically; now called Zebra Agate), etc. Onyx does not exhibit opalescence.
Agate and Onyx are distinguished by the color banding; agate has curved bands, Onyx has parallel bands. Both are members of the chalcedony group of silicate minerals