Overview

Olivenite is a copper arsenate hydroxide, Cu2(AsO4)(OH), and one of the quintessential secondary copper minerals from the oxidized zones of arsenic-bearing ore deposits. Its name reflects its distinctive olive to yellow‑green color, although crystals can range from rich bottle‑green to brownish hues. It crystallizes in the orthorhombic system and occurs in a variety of attractive habits: sharp prismatic crystals, delicate acicular sprays, radiating hemispheres, botryoidal crusts, and velvety coatings. Luster is typically vitreous to silky on fibrous forms, and the best crystals can be strikingly bright for a copper secondary.

Collectors value olivenite for the combination of vivid color, varied habits, and its occurrence at world‑class classic localities. Historic Cornish mines produced archetypal crystallized specimens in the 18th–19th centuries; later, Tsumeb and Cap Garonne contributed superb modern classics. Associations are part of the charm: olivenite frequently accompanies conichalcite, duftite, adamite, clinoclase, chalcophyllite, liroconite, cornwallite, malachite, azurite, scorodite, and iron oxides. While individual crystals are usually small (millimeters), the species excels in aesthetics through fine sprays, radiating groups, and richly colored, contrasting matrix pieces.

Popularity

Olivenite enjoys steady demand among both micromounters and cabinet collectors. Its historical pedigree from Cornwall appeals to classic locality enthusiasts, while photogenic modern pieces from Tsumeb and Cap Garonne draw aesthetics‑driven collectors. Prices vary widely: attractive micromounts and small sprays are accessible, but undamaged, well‑composed matrix specimens from benchmark localities—especially Cornwall with provenance, or robust Tsumeb crystals with contrast—can be expensive. Interest is also boosted by its relationship to the zinc‑rich analogue zincolivenite, which can form solid solutions at some deposits; pieces showing compositional or color transitions add scientific and collector intrigue.

Top Collecting Localities

While olivenite occurs broadly, a handful of localities set aesthetic and historical standards.

Wheal Gorland, Cornwall, UK

Among the most storied olivenites ever found, Wheal Gorland (St Day area, Cornwall) produced superb 18th–19th century classics. Expect sharp, slender prismatic crystals and radiating sprays in rich olive to deep green, commonly perched on gossanous or quartz‑rich matrix. Associations with Cornish arsenates—clinoclase, cornwallite, chalcophyllite—and occasional liroconite or malachite give coveted color contrast. Though usually small, the best groups are exceptionally well‑formed and extremely rare in pristine condition; provenance and period labels significantly enhance value. Intact, undamaged micro to small‑cabinet pieces from Gorland are considered reference material for the species.

Tsumeb Mine, Namibia

Tsumeb delivered some of the most vibrant and three‑dimensional olivenites, typically from the oxidation and secondary enrichment zones. Crystals range from lustrous prismatic individuals to radiating sprays and dense carpets, often on contrasting white calcite/dolomite or dark iron‑oxide matrix. Color can be rich bottle‑green to yellow‑green, with superior luster compared to many localities. Associations with duftite, conichalcite, malachite, azurite, smithsonite, and quartz are common, and some pieces show compositions trending toward zincolivenite, of interest to specialists. Tsumeb matrix clusters with sharp, undamaged terminations are centerpiece‑quality and are among the most sought after modern olivenites.

Collector’s Guide

Evaluating Specimen Quality

• Color and Luster:

  • The most desirable olivenites show saturated olive to bottle‑green hues with strong vitreous or silky luster. Bright, even color on exposed crystal faces or radiating sprays is ideal.
  • Brownish or dull surfaces are common on altered or etched material; prioritize fresh, glossy terminations and clean, vivid aggregates.

• Crystal Habit and Aesthetics:

  • Prismatic crystals with sharp faces and distinct terminations are relatively scarce and prized (notably Cornwall and Tsumeb).
  • Radiating sprays and hemispherical aggregates can be superbly aesthetic, especially when centered in a vug with pleasing symmetry.
  • Matrix contrast elevates appeal: green olivenite on white carbonate, pale quartz, or rusty gossan “pops.” Association with complementary species (e.g., duftite, conichalcite, clinoclase, chalcophyllite) adds both value and visual interest.

• Size and Composition:

  • Individual crystals are typically minute to a few millimeters; clusters and vug linings can fill small cavities. Exceptional larger crystals are rare and command strong prices.
  • At compositionally variable deposits (e.g., Tsumeb), pieces near the olivenite–zincolivenite join can show subtle color variations; documented analyses or expert attributions are meaningful to specialists.

• Condition:

  • Sprays and fibrous hemispheres are fragile. Look closely for crushed tips, missing sectors in vugs, or shed needles.
  • Gossan matrices can be friable. Prefer specimens with solid, well‑trimmed bases and undisturbed cavity linings.
  • Historical Cornish and Chessy pieces often show old contacts or edge wear; minor, non‑distracting wear may be acceptable given rarity and provenance.

• Provenance:

  • Labels from classic collections and period documentation significantly enhance desirability, particularly for Wheal Gorland, Chessy, and early Tsumeb.

Detecting Repairs or Treatments

• Repairs:

  • Vug linings and delicate sprays are sometimes stabilized or spot‑glued where matrix was friable. Inspect cavity edges and the backs for glossy adhesive residues or different surface sheen.
  • Prismatic crystals reattached to matrix may show a thin glue line or slight misalignment. A 10x loupe and oblique light help reveal joins.

• Cleaning and Alterations:

  • Avoided in quality collections, but some pieces may have been rinsed in mild chemicals to reduce iron staining; over‑cleaning can dull luster.
  • Dyeing or coatings are unusual for olivenite; if a surface looks unnaturally uniform or “plastic,” scrutinize under magnification.

As always, disclosure from reputable dealers and a careful loupe inspection reduce surprises.

Care and Storage

Olivenite contains arsenic; handle responsibly and avoid creating or inhaling dust.

• Handling:

  • Use gentle, minimal handling—especially with acicular sprays and vug linings. Support matrix pieces with both hands.
  • Wash hands after handling and avoid touching your face. Keep away from children and pets.

• Light, Heat, and Environment:

  • Colors are generally light‑stable, but avoid prolonged direct sunlight and high heat, which can stress matrix or adhesives and risk dehydration of delicate surfaces.
  • Maintain moderate, stable humidity; very dry air can embrittle some gossans and loosen old glues.

• Cleaning:

  • Prefer dry methods: a soft artist’s brush, hand blower, or very gentle air bulb to remove dust.
  • If necessary, a brief rinse in distilled water with a drop of mild dish soap; avoid soaking. Do not use acids or aggressive cleaners—copper arsenates are susceptible to dissolution/alteration.
  • Avoid ultrasonic and steam cleaners; vibrations and heat can shatter sprays or detach crystals.

• Storage and Display:

  • House in padded boxes or in a display with stable mounts/tack. Ensure vug‑facing pieces are supported to prevent shedding.
  • Do not store in contact with harder specimens that could abrade crystal tips; conversely, olivenite can scratch softer species—separate with foam or tissue.
  • For micromounts, closed capsules prevent dust and reduce handling; for cabinets, consider a dust‑tight case and gentle LED lighting.

By prioritizing minimal handling, mild cleaning, and stable conditions, olivenite’s rich greens and delicate architectures will remain attractive for decades.