Shattuckite: Formation, Geology & Varieties

Shattuckite: Formation, Geology & Varieties

Shattuckite: Formation, Geology & Varieties

Cu5(SiO3)4(OH)2 — a saturated sky‑ink copper silicate born in the oxidized zone, famous for silky radial sprays, quartz-hosted phantoms, and pseudomorphs after malachite.

Creative catalog aliases: Azure Scribe • Lagoon Cipher • Sky‑Ink Vein • River Glyph • Cobalt Quill • Kaoko Night‑Blue • Ajo Sky‑Script • Tide‑Thread

💡 What It Is — Geology in One Breath

Shattuckite is a secondary copper silicate hydroxide that crystalizes in the orthorhombic system and typically appears as silky, radial spherulites of acicular crystals. It forms in the near‑surface oxidized zones of copper deposits and is classically associated with quartz, chrysocolla, malachite, and ajoite. The species was first described from the Shattuck Mine, Bisbee, Arizona, where it famously occurs as pseudomorphs after malachite. :contentReference[oaicite:0]{index=0}

Catalog shorthand: Secondary Cu silicate • orthorhombic • silky spherulites • oxidized Cu zone • common with quartz/chrysocolla/malachite • type locality: Bisbee (AZ). :contentReference[oaicite:1]{index=1}

🧪 How It Forms — A Step‑by‑Step Story from the Oxidation Zone

  1. Weathering primes the system. Near the surface, copper sulfides (like chalcopyrite, bornite, chalcocite) oxidize. Copper migrates and first precipitates as secondary carbonates such as malachite/azurite in open fractures and vugs. (This is the classic “oxidized zone” framework for many blue‑green copper minerals.) :contentReference[oaicite:2]{index=2}
  2. Silica‑rich fluids arrive. When silica‑bearing fluids circulate through those same cavities, copper can be fixed as silicates rather than carbonates — including shattuckite, often alongside chrysocolla and ajoite. :contentReference[oaicite:3]{index=3}
  3. Replacement & pseudomorphs. At Bisbee, shattuckite locally replaces malachite while preserving the original malachite crystal shapes — textbook pseudomorphism that makes wonderful teaching specimens. :contentReference[oaicite:4]{index=4}
  4. Captured by quartz. In some deposits (notably Kaokoveld, Namibia), shattuckite forms felted, radial layers on growing quartz crystals and then becomes trapped as blue phantom planes when quartz overgrows — the source of coveted “shattuckite‑in‑quartz.” :contentReference[oaicite:5]{index=5}

Quick memory hook for tours: Carbonates first, then silicates, then quartz does the housekeeping. (Geology’s version of “clean your room before company arrives.”)

🌍 Geologic Settings & Teaching Localities

Kaokoveld Plateau, Namibia

Secondary copper mineralization in quartz veins within Otavi carbonates; celebrated for dioptase, plancheite, and shattuckite, including quartz‑hosted phantoms and drusy coatings. Local spots include Kandesei and Omaue. :contentReference[oaicite:6]{index=6}

Shattuck Mine, Bisbee, Arizona (USA)

Type locality; shattuckite occurs as pseudomorphs after malachite and as small spherules — the place that gave the mineral its name. :contentReference[oaicite:7]{index=7}

New Cornelia Mine, Ajo, Arizona (USA)

Known for shattuckite that is sometimes included in quartz; it’s part of the broader Arizona oxidized‑copper story. :contentReference[oaicite:8]{index=8}

Milpillas Mine, Sonora (Mexico)

Modern copper mine with attractive shattuckite and shattuckite + quartz associations; adds a useful contrast to Namibian textures. :contentReference[oaicite:9]{index=9}

Wider distribution also includes Tsumeb (Namibia) and Katanga (DRC) — classic oxidized copper provinces where silica‑rich late fluids roam the fracture network. :contentReference[oaicite:10]{index=10}

🔬 Paragenesis, Textures & Associations (What to Look For)

Silky radial spherulites

Shattuckite most often builds acicular, radiating clusters with a satiny sheen; under a loupe they look like tight starbursts or “painted felt.” :contentReference[oaicite:11]{index=11}

Botryoidal & crusty coatings

Rounded, velvety coatings over matrix; common where fluids repeatedly wet cavity walls. (Great “lagoon” look in cabinet pieces.) :contentReference[oaicite:12]{index=12}

Pseudomorphs after malachite

Replacement preserves external malachite forms while swapping the chemistry and texture for shattuckite — a paragenetic snapshot in 3D. :contentReference[oaicite:13]{index=13}

Quartz‑hosted “phantoms”

Blue phantom layers or plumes inside quartz: shattuckite deposited on crystal faces, then captured as the quartz continued to grow. :contentReference[oaicite:14]{index=14}

Typical associates: quartz, chrysocolla, malachite, ajoite (and locally dioptase, plancheite), reflecting the silica‑rich evolution of Cu‑bearing solutions. :contentReference[oaicite:15]{index=15}

💎 Varieties — Geology‑Truthful, Shop‑Ready Types

These are habits and assemblages you’ll encounter in the field and in the trade; they’re not separate species but they do deserve distinct labels.

1) Azure Loom (Radial Spherulites)

Silky, radiating, deep‑blue spherulites on matrix. Great for teaching acicular growth in oxidized zones. :contentReference[oaicite:16]{index=16}

Localities: Bisbee (AZ); Kaokoveld (Namibia). :contentReference[oaicite:17]{index=17}

2) Lagoon Drapery (Botryoidal/Crusty)

Velvety coatings, often mingled with chrysocolla/malachite for painterly blues and greens. :contentReference[oaicite:18]{index=18}

3) Malachite’s Mask (Pseudomorphs)

Shattuckite replacing malachite while retaining the malachite’s outward crystal shape — a “mineral costume change.” :contentReference[oaicite:19]{index=19}

4) Sky‑Ink in Glass (Shattuckite‑in‑Quartz)

Blue phantoms/veils trapped in clear quartz; photogenic and more durable for jewelry. :contentReference[oaicite:20]{index=20}

Seen notably in Kaokoveld and Ajo. :contentReference[oaicite:21]{index=21}

5) Blue‑on‑Blue Twins (with Plancheite)

Intimate intergrowths with plancheite — another Cu silicate — but note the contrast: plancheite is harder (≈5.5–6) and lacks obvious cleavage whereas shattuckite is softer (~3.5) with perfect cleavage on {010}/{100}. :contentReference[oaicite:22]{index=22}

6) Lagoon Map (with Chrysocolla/Malachite)

Veins and patches of shattuckite amid chrysocolla and malachite, sometimes with dioptase accents — a textbook oxidized‑copper palette. :contentReference[oaicite:23]{index=23}

🏷️ Trade Names & Mixed Material (Know What You’re Seeing)

  • “Shattuckite‑in‑Quartz” — a descriptive, geology‑accurate term for quartz crystals or druses hosting blue shattuckite planes/plumes. It reflects real growth history (deposition → overgrowth). :contentReference[oaicite:24]{index=24}
  • “Quantum Quattro (Silica)” — informal market name for mixed copper minerals in a quartz matrix (typically some combination of chrysocolla, malachite, shattuckite, dioptase, often smoky quartz). Not a species; composition varies by piece and seller. Use descriptive labeling alongside the trade name. :contentReference[oaicite:25]{index=25}
  • Stabilized composites — Some decorative material (notably from parts of the DRC) has been reported resin‑stabilized to improve hardness/polish. Disclose when known; look for filled pits and unusually glossy fracture surfaces. :contentReference[oaicite:26]{index=26}
Labeling tip: For mixed pieces, pair a creative name with a factual subtitle — e.g., “Lagoon Cipher (shattuckite + chrysocolla + quartz composite, Kaokoveld)”.

❓ FAQ (Collector Notes)

Is shattuckite always fibrous?

Fibrous acicular growth in radial clusters is most common, but you’ll also see crusty/botryoidal coatings and massive seams. In polished slabs, the “felted” texture shows as mottled blue fields. :contentReference[oaicite:27]{index=27}

How do I tell shattuckite from plancheite in a mixed blue mass?

In hand specimen: shattuckite is softer (~3.5) with perfect cleavage on two planes; plancheite is significantly harder (~5.5–6) and typically shows no obvious cleavage. Under the scope, their optics diverge (shattuckite: higher RIs ~1.75–1.82). When in doubt, Raman solves it. :contentReference[oaicite:28]{index=28}

Why is “shattuckite‑in‑quartz” so popular?

Quartz protects the soft, cleavable blue mineral and creates dramatic phantoms that trace crystal growth — essentially a time‑lapse of the pocket. Plus, it photographs like a dream. :contentReference[oaicite:29]{index=29}

✨ The Takeaway

In the life of a copper deposit, shattuckite is the moment when silica‑bearing, oxygen‑rich waters paint the cavities blue — sometimes replacing earlier malachite, sometimes laying down a felted veil only to be sealed in quartz as the pocket matures. Its varieties are simply chapters of that same story: radial spherulites, botryoidal drapes, pseudomorphs, and phantoms in glass. Label them clearly, name them creatively, and your readers (and shelves) get both science and sparkle.

Lighthearted wink: If quartz is the museum curator, shattuckite is the bold blue artist whose work gets framed for future generations. 😄

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