Opal
On the label: Opal · Gemstone
What it is
Hydrated silica that diffracts light into play-of-color. Mohs 5.5 to 6.5 and contains water, so it cracks with heat and dryness; doublets and triplets (thin opal glued to a backing) are common and must be described as such.
Gemstones: Natural gemstones, as mined and cut. Hardness (Mohs scale) says what scratches what; treatment (heat, oil, dye) must be disclosed under FTC rules.
Wikidata: Silica mineraloid. Q171058 →
In the research
41 PubMed papers mention it with jewelry, allergy, eyewear or UV; the three most recent:
- Elevated RIPK2 Expression in Atopic Dermatitis Skin Is Associated with Mixed Th1/Th2 Cytokine Responses in CD4(+) T Cells · International journal of molecular sciences, 2026
- Information Security with Smart Hydrogels: Photo-Patterning and Multi-Stimuli Responsive Structural Color · Nano-micro letters, 2026
- Ultra-robust spin-assisted infiltration for large-area, highly ordered, defect-free titanium dioxide and tin dioxide inverse opal frameworks toward efficient ultraviolet-visible ph · Journal of colloid and interface science, 2026
A paper is a paper, not a verdict: titles are listed so you can read them, and a study on one fabric or one filter says little about the piece in your hand.
Other gemstones
Clasp & Lens describes materials from the public record and does not appraise, grade or test pieces; what a listing states is the supplier's statement. If a piece causes a rash, take it off; a reaction that spreads or blisters is a doctor's question, and sunglasses are no substitute for impact-rated eye protection where that is required.