Overview

Arsenopyrite (FeAsS) is the classic steel-gray, strongly metallic arsenic sulfide and the primary ore of arsenic. It forms sharply striated prismatic crystals with wedge-shaped terminations and superb, mirror-bright luster. Habit ranges from single robust prisms to dramatic radiating clusters and intergrown sheaves. Aesthetics often come from contrasts: silvery arsenopyrite perched on snow-white quartz, set amid tan siderite, or paired with pastel fluorite or green fluorapatite. Good crystals commonly measure 2–6 cm, with larger individuals from a few key districts.

For collectors, arsenopyrite offers sculptural geometry, heft (it is notably dense), and a refined metallic sheen that can rival pyrite or stibnite. While many cabinet specimens remain quite affordable, top-end pieces—particularly from Panasqueira (Portugal), select Chinese finds (Yaogangxian, Dachang), Dalnegorsk (Russia), and historic European classics (Freiberg, Trepča)—command strong prices. Fresh, damage-free terminations and untarnished surfaces make a big difference.

Popularity

Arsenopyrite is a staple of serious sulfide suites and old European vein collections, prized for crystalline perfection and history. Its popularity surged with major European mining districts (Freiberg and the Balkans), then again with the great Panasqueira specimens of the mid- to late-20th century, and later with the wave of fine Chinese material from the 1990s–2010s. Because arsenopyrite plays well visually with quartz, fluorite, siderite, and fluorapatite, it anchors many mixed-matrix display pieces.

All levels of collectors can participate: sharp thumbnails are abundant; elegant small cabinets remain reasonably priced; and museum-caliber matrix groups with multiple perfect terminations are rare and chased. Though it lacks bright colors, its metallic brilliance, classic associations, and strong locality stories keep demand steady. As with many sulfides, provenance and condition heavily influence desirability.

Top Collecting Localities

Below are renowned sources known for producing arsenopyrite specimens with distinctive aesthetics or historical importance. Each locality is included only if a verified EarthWonders locality ID is available.

Panasqueira Mines, Portugal

Panasqueira is the world’s most celebrated arsenopyrite locality. Specimens are instantly recognizable: sharply striated, lustrous silvery crystals—often 2–8 cm—set with snow-white quartz, tan to honey siderite, and brilliant green fluorapatite. The pieces are architectural and balanced, typically with multiple crystals oriented in dynamic clusters and excellent contrast. Many of the finest matrix specimens of the species come from here; they established the modern aesthetic standard and remain benchmarks.

Yaogangxian Mine, China

The Yaogangxian skarn-vein system produced elegant arsenopyrite in association with pastel fluorite, quartz, and visible tungsten minerals. Crystals are typically sharp, highly reflective, and well-isolated, often forming attractive small cabinet pieces with excellent geometry. Peak production in the late 1990s–2000s brought a steady flow of quality pieces; select specimens with fluorite cubes or octahedra can be spectacular.

Trepča Stari Trg Mine, Kosovo

The Trepča complex is a classic European district, and Stari Trg produced robust arsenopyrite crystals on attractive sulfide and carbonate matrices. Crystals tend to be stout and bright, often framing sphalerite, pyrite, and calcite for dramatic contrast. Vintage specimens with original labels are coveted for their history; modern pieces remain respected for size and balance.

Collector’s Guide

Evaluating Specimen Quality

• Color and Luster: The species should present as bright silvery to steel-gray with strong metallic luster. Fresh, mirror-like faces are ideal; a dull or brownish film indicates tarnish or minor oxidation. Lightly iridescent patina can be attractive, but deep, patchy tarnish usually detracts.
• Crystal Form and Size: Look for sharply defined prismatic crystals with characteristic longitudinal striations and clean wedge-like terminations. Panasqueira-style clusters with multiple orientations and attractive associations (quartz, fluorapatite, siderite) are especially prized. Single crystals of 2–5 cm are common on quality pieces; larger, undamaged crystals from marquee localities are scarce and valuable.
• Terminations and Striations: Undamaged tips matter greatly—blunt or chipped terminations reduce value unless compensated by rarity, size, or aesthetic impact. Crisp, continuous striations that align along the prism are a plus.
• Matrix and Associations: Contrasting, stable matrices elevate value. Panasqueira combinations (quartz + siderite + fluorapatite) and Chinese assemblages (quartz + fluorite + cassiterite) are favorites. Ensure the crystal/matrix junctions are natural and not glued (see “Detecting Repairs or Treatments”).
• Condition: Arsenopyrite is brittle. Inspect for edge nicks, micro-chatter, or cleaved backs. A tiny inconspicuous ding may be acceptable on a superb piece, but perfection commands a premium.
• Aesthetics: As with most metallics, “architecture” wins—balanced composition, separation between crystals, clean display angle, and attractive contrasts. A piece that displays well without special lighting and shows reflectivity across faces will stand out.

Detecting Repairs or Treatments

• Reattachment and Repairs: Because crystals often separate in the pocket, reattachments are not uncommon. Check for:
  • Straight, planar join lines across a crystal.
  • Misaligned striations or minute offsets.
  • Thin glue films at the base or along a crack (some epoxies fluoresce under LW-UV).
• Polishing: Polished “terminations” or overly glossy ground surfaces are red flags. Natural faces show fine growth marks/striations; a mirror-flat facet at an odd angle may be fabricated.
• Cleaning and Coatings: Harsh acid cleaning can leave etched, matte patches. Occasionally, a microcrystalline wax or oil is applied to minimize tarnish; look for uneven sheen or residue in recesses. Ask for disclosure—reputable dealers will tell you.

Care and Storage

Arsenopyrite contains arsenic. Normal handling is safe, but treat it with respect.

• Handling and Safety:
  • Do not grind, saw, or heat. Cutting or heating releases hazardous arsenic-bearing dust/fumes.
  • Wash hands after handling; keep out of reach of children and pets.
  • When trimming nearby matrix, use eye/respiratory protection and minimize dust.
• Environment:
  • Store in a dry, stable environment. Like many sulfides, arsenopyrite can tarnish or alter in high humidity, sometimes forming secondary arsenates (e.g., scorodite) on reactive surfaces.
  • Use enclosed cabinets with desiccant (silica gel) in humid climates. Avoid proximity to acidic vapors (new wood, certain foams).
• Light and Temperature:
  • Normal display lighting is fine. Avoid prolonged sunlight heating; do not place over hot case lights. Never heat the specimen.
• Cleaning:
  • Dust with a soft brush or air bulb. If needed, brief rinses in distilled water with a drop of mild soap, then dry thoroughly.
  • Avoid acids and aggressive cleaners; avoid ultrasonic cleaners (brittle sulfide, potential to initiate microcracks or loosen repairs).
  • If minor tarnish develops, professional preparators can sometimes improve luster with careful, non-destructive methods—seek expert help rather than experiment.
• Mounting and Transport:
  • Support from below; do not pinch terminations. Use a small amount of mineral tack for display stability.
  • For shipping, immobilize with soft foam and avoid crystal-to-crystal contact. The species is heavier than it looks—pack accordingly.

By prioritizing sharp form, pristine surfaces, and attractive associations—especially from the classic localities above—you can assemble an arsenopyrite suite that shines with metallic elegance and historical depth.