Shattuckite: Physical & Optical Characteristics

Shattuckite: Physical & Optical Characteristics

Shattuckite: Physical & Optical Characteristics

Cu5(SiO3)4(OH)2 — a rare, saturated‑blue copper silicate whose silky fibers and sky‑ink color make it a favorite for study slabs, cabs, and “Shattuckite‑in‑Quartz” décor 💙

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

💡 What Is Shattuckite?

Shattuckite is a copper silicate hydroxide (formula Cu5(SiO3)4(OH)2) that crystallizes in the orthorhombic system. It is a secondary mineral of the oxidized copper zone, famed for saturated blues and silky, fibrous textures. First described at the Shattuck Mine in Bisbee, Arizona (its type locality), it commonly occurs with chrysocolla, malachite, plancheite, dioptase, and quartz; in some deposits it forms striking pseudomorphs after malachite and beautiful “Shattuckite‑in‑Quartz” composites. :contentReference[oaicite:0]{index=0}

One‑liner for product pages: “Shattuckite — sky‑ink copper blue with a silky whisper.”

📏 Physical & Optical Specs — At a Glance

Property Shattuckite (Cu5(SiO3)4(OH)2) Notes
Chemical group Copper silicate (inosilicate); hydroxide Secondary mineral in oxidized Cu deposits.
Crystal system Orthorhombic Often as fibrous/spherulitic aggregates.
Color Deep to light blue; turquoise‑blue; sometimes mottled with green associates Color from Cu2+ centers in silicate lattice.
Streak Blue Helpful vs. chrysocolla’s white‑to‑blue‑green streak.
Luster Dull to silky; satiny on fibrous faces Polish can be waxy‑gloss on cab surfaces.
Transparency Translucent → opaque (rarely transparent in fibers) Gemmy look when thinly included in quartz.
Hardness (Mohs) ~3.5 Soft; favor protective settings for jewelry.
Cleavage Perfect on {010} and {100} Planar partings make slabs delicate.
Fracture / Tenacity Uneven; brittle; splintery on fibers Avoid torque on narrow pieces.
Specific gravity ~4.1 (meas. ≈4.11) Hefty compared to many blue “look‑alikes.”
Optical character Biaxial (+) Pleochroic blue tones along axes.
Refractive indices nα ≈ 1.753 • nβ ≈ 1.782 • nγ ≈ 1.815 Birefringence δ ≈ 0.062 (conspicuous under polars).
Pleochroism X very pale blue • Y pale blue • Z deep blue Rotate stage for color change test.
Fluorescence Generally inert Not a diagnostic effect.
Solubility / chemicals Avoid acids & harsh cleaners Copper silicates can etch or dull.
Catalog shorthand: Cu5(SiO3)4(OH)2 • orthorhombic • Mohs ~3.5 • SG ~4.1 • perfect {010},{100} • biaxial(+) • n≈1.753–1.815 • δ≈0.062 • pleochroic blue. Key data summarized from mineral handbooks and reference entries. :contentReference[oaicite:1]{index=1}

🔬 Optical Behavior — why shattuckite’s blue looks “inked”

Shattuckite’s high refractive indices (about 1.75–1.82) and strong birefringence (δ≈0.062) give it a dense, ink‑blue presence in hand specimen and a lively response under crossed polars. Expect pronounced pleochroism: rotate a thin section or a polished cab under a penlight and watch the hue shift from very pale to deep blue along optic directions — a quick, satisfying field check. :contentReference[oaicite:2]{index=2}

Show‑and‑tell: Under a loupe, side‑light silky radial sprays; in polarized scope, note first‑ to high‑order interference colors from fibrous areas.

🎨 Color & Stability — saturated copper blues

  • Hue & tone: Deep royal to lagoon‑blue; can intermix with green associates (malachite/chrysocolla) for “map‑like” patterns.
  • Light: Indirect daylight preserves blues best; prolonged hot case lights can sap luster on fibrous faces.
  • Quartz composites: When included in quartz (“Shattuckite‑in‑Quartz”), color gains depth and durability — popular for cabs and décor pieces. :contentReference[oaicite:3]{index=3}
Display tip: Photograph on mid‑gray or charcoal; cool LEDs maintain true blue without warming toward teal.

🔷 Crystal Habit & Common Textures

Spherulitic & Radiating Fibers

Sprays of acicular crystals in rounded clusters; silky to satiny sheen; classic “sky‑ink” look in vugs and along seams. :contentReference[oaicite:4]{index=4}

Botryoidal/Crusty Masses

Rounded coatings and vein fill; often intergrown with chrysocolla or plancheite for mixed‑blue surfaces. :contentReference[oaicite:5]{index=5}

Pseudomorphs

Locally replaces malachite while preserving its external shape — a mineral “costume change” that fascinates collectors. :contentReference[oaicite:6]{index=6}

Quartz Composites

Fine blue veins and plumes suspended in clear quartz from locales like Ajo, AZ and Milpillas, MX — excellent cabbing material. :contentReference[oaicite:7]{index=7}

Associations: chrysocolla, malachite, azurite, plancheite, dioptase, cuprite, quartz — classic oxidized copper assemblages. :contentReference[oaicite:8]{index=8}

🧭 Identification: quick tests & look‑alikes

Simple field checks

  • Heft: SG ~4.1 — surprisingly heavy for a blue stone.
  • Hardness: ~3.5 (knife will mark; softer than glass).
  • Cleavage: perfect on two planes ({010}, {100}); watch for plate‑like parting.
  • Streak: blue (distinct from many look‑alikes).

Shattuckite vs. Plancheite

Both are fibrous copper silicates, but plancheite is distinctly harder (Mohs ~5.5–6), with lower typical RIs (≈1.64–1.74) and no observed cleavage. Shattuckite’s perfect cleavage and higher RIs (~1.75–1.82) stand out. :contentReference[oaicite:9]{index=9}

Shattuckite vs. Chrysocolla

Chrysocolla is usually softer (Mohs ~2.5–3.5 average, but variable), lighter (SG ~2.0–2.4), and often amorphous/cryptocrystalline with no cleavage. Shattuckite is heavier, has perfect cleavage, and shows higher RIs. :contentReference[oaicite:10]{index=10}

Other blues

Azurite (hardness ~3.5–4, effervesces slowly in acid), dioptase (hardness ~5, vivid emerald‑green), and blue smithsonite (SG ~4.3, good rhombohedral cleavage) may appear nearby; use hardness/SG/cleavage to separate.

Lab bench: Refractive indices ~1.753–1.815; biaxial(+) with marked pleochroism; δ≈0.062. These optical values are highly diagnostic for shattuckite. :contentReference[oaicite:11]{index=11}

🧼 Care, Display & Shipping (soft & cleavable)

  • Handling: Support from the base; avoid prying stress across cleavage planes.
  • Cleaning: Soft brush + dry air bulb. If needed, quick lukewarm rinse with mild soap; pat dry immediately.
  • Chemicals: Avoid acids/solvents — copper silicates can etch or lose luster.
  • Jewelry: Best as pendants/earrings, protected cabs, or set inside quartz; rings need bezel protection and mindful wear.
  • Shipping: Immobilize completely; cushion between fibers/plates; label Fragile — Perfect Cleavage.

Care analogy: treat shattuckite like a fancy notebook with very nice pages — gorgeous color, but don’t bend the spine. 😉

📸 Photographing Shattuckite (make the blue sing)

  1. Light: Diffuse key light + cool fill; avoid warm bulbs that tilt blue toward teal.
  2. Backgrounds: Mid‑gray for true blue; light wood or slate for “field note” vibes.
  3. Polarizer: A CPL tames glare on satin fibers without flattening the color.
  4. Angles: Tilt to catch pleochroic depth; side‑light radial sprays to show texture.
  5. Quartz pieces: Backlight lightly to float the blue plumes inside the host.
Caption template: “Shattuckite (Cu5(SiO3)4(OH)2) — silky orthorhombic fibers; biaxial(+) with strong blue pleochroism; perfect {010}/{100} cleavage.”

❓ FAQ

Is shattuckite the same as chrysocolla?

No. Both are copper silicates, but chrysocolla is typically softer, lighter, and often amorphous/cryptocrystalline with no cleavage; shattuckite is heavier (SG ~4.1), shows perfect cleavage on two planes, and has higher refractive indices. :contentReference[oaicite:12]{index=12}

What about plancheite — why do people confuse them?

Both can be fibrous copper blues in the same deposits. But plancheite is harder (≈5.5–6), lacks obvious cleavage, and has somewhat lower RIs; microscope/lab work resolves the pair easily. :contentReference[oaicite:13]{index=13}

Where does the best material come from?

Type material is from the Shattuck Mine (Bisbee, Arizona); many collectors also prize specimens and cabs from Namibia’s Kaokoveld and from Milpillas, Sonora (Mexico) — including shattuckite‑in‑quartz. :contentReference[oaicite:14]{index=14}

Does shattuckite fluoresce?

It is generally non‑fluorescent; fluorescence is not used for identification.

✨ The Takeaway

Shattuckite is a copper silicate hydroxide with unmistakable ink‑blue color, silky to satiny textures, and diagnostic optics (high RIs, strong birefringence, blue pleochroism). It’s soft (Mohs ~3.5) with perfect cleavage, so treat specimens gently — or enjoy the color protected within quartz. For catalogs, pair its science‑true name with creative nicknames (Azure Scribe, Sky‑Ink Vein) and you’ll have pages that are both accurate and memorable.

Lighthearted wink: It’s the mineralogical equivalent of fountain‑pen ink — beautiful, saturated, and happiest when you don’t press too hard. 😄

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