Coral - www.Crystals.eu

Coral

Coral • Organic Gem Skeleton: CaCO3 (Calcite/Aragonite) or Protein (Black Coral) Mohs ~3–4 (precious) • ~6.5–7 (fossil/agatized) Porous • Sensitive to Chemicals

Coral ❤️ — Ocean Architecture Turned Wearable Art

From reef‑builders to heirloom beads, coral bridges biology and jewelry. (It’s the only gemstone that once threw a great beach party.)

Coral is an organic gem: the hard skeleton from colonies of tiny marine animals called polyps. For millennia, people have carved, strung, and set coral in jewelry—especially the red‑to‑pink “precious corals”, elegant angel‑skin tones, and dramatic black coral. Today you’ll also meet blue coral, dyed bamboo coral (used to emulate red tones), and fossil/agatized coral with mesmerizing flower patterns. This concise field guide covers types, identification, care, and design history—plus a couple of light jokes to keep the tide cheerful.

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Hardness
Precious: ~3–4 • Black: ~3 • Fossil (silica): ~6.5–7
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Care Level
Gentle—avoid acids, heat, ultrasonic, steam
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Color Family
Deep red, salmon, blush, cream, black, blue, fossil “flowers”

What It Is (Gemology in a Nutshell) 🔬

Organic Gem

Unlike minerals, coral is built by animals. Each polyp secretes a skeleton: usually calcium carbonate (calcite or aragonite). Some (like black coral) have a horny protein skeleton instead.

Precious vs. Decorative

Precious coral is the red‑pink branchy material used in fine jewelry. Decorative corals include blue, bamboo, sponge, and fossil/agatized coral—each with its own look and care needs.

Why It Matters

Crisp color, satin luster, and a uniquely warm presence. Coral makes strands glow, carvings pop, and rings read vintage‑romantic or modern‑minimal, depending on cut.

Think of coral as ocean architecture—with great taste in color palettes.

Types & Trade Names (Side‑by‑Side) 🧭

Type Skeleton Typical Colors Mohs Trade Notes & Common Treatments
Precious Red/ Pink Coral (e.g., Corallium spp.) Calcite (dense, fine‑grained) Deep red (“aka”), red‑orange (“momo”), soft blush (“angel skin”) ~3–4 Often selected for even, saturated color. Color may be gently lightened or stabilized; note any treatments in records.
Black Coral (Antipatharians) Horny protein (not carbonate) Black to deep brown ~3 Polishes to a mirror; often carved or beaded. Keep away from heat/solvents.
Blue Coral (Heliopora) Aragonite (with iron giving blue cast) Steel‑blue to gray‑blue ~3–3.5 Porous; often stabilized. Frequently used in cool‑toned design palettes.
Bamboo Coral (Isididae) Calcite segments + protein nodes Natural cream; frequently dyed red ~3–4 Used to emulate red tones when dyed. Record dye treatment in catalog notes.
Sponge/“Spongy” Coral Porous coral skeleton Usually dyed red/orange ~3–4 Stabilized with resin to take a polish; open texture is part of the character.
Fossil / Agatized Coral Original coral replaced by silica (chalcedony) Neutrals to honey, gray, mocha; “flower” patterns ~6.5–7 Durable, takes a bright polish; often cut as cabochons, spheres, and display plates.
Specimen label examples (reference format): “Corallium spp., cabochon, natural pale pink (‘angel‑skin’); locality: Italy or Japan (if known).” “Fossil (agatized) coral — chalcedony replacement with ‘flower’ corallites; locality: Indonesia or Florida.”

Colors, Textures & ID Clues 🎨

Precious Coral Surface

  • Even color from skin to core in premium pieces; some show lighter cores (not a flaw, just natural).
  • Silky luster—less glassy than agate, warmer than shell.
  • Under magnification, faint growth striae, occasional tiny pits at branch centers.

Fossil Coral Patterns

  • “Flower” rosettes = ancient corallites in cross‑section.
  • Colors from cream/gray to mocha/amber; sometimes subtle pinks.
  • Chalcedony glow with quartz micro‑crystals in cavities.
Quick ID: Dyed bamboo coral often shows color concentrated in pores and near drill holes; precious coral color tends to be more uniform, with a denser feel and finer polish.

Evaluation & Considerations 🧰

Color & Evenness

  • Red precious: Deep, even color (“aka”) is less frequently observed in larger specimens.
  • Angel skin: Soft, clean blush without gray/brown cast.
  • Fossil: High‑contrast, well‑defined “flowers.”

Clarity & Texture

  • Fewer pits, chips, and surface fills suggest careful finishing and denser structure.
  • For sponge/bamboo, tidy stabilization yields smoother polish and wearability.

Cut & Scale

  • Cabochons: Even dome; no thin edges.
  • Beads: Roundness, matched color, clean drill holes.
  • Carvings: Crisp lines, protected high points.

Terms & Treatments (explained)

  • Dyed Color added to achieve a bold red or uniform tone; common for bamboo/sponge.
  • Lightened Gently paled to reach soft blush (“angel‑skin”) shades.
  • Stabilized Resin fills pores for a smoother, more durable surface.
  • Trade names “aka” = deep red, “momo” = red‑orange, “angel‑skin” = very pale pink.
  • Provenance Where collected or worked; context for study and cataloging when known.

Cataloging & Notes

For collection labels, record type/species (if known), treatment state, and locality or workshop when available.

“Corallium japonicum, cabochon, natural color, 12×10 mm; carved; Japan workshop, mid‑20th c.”

Occurrence in collections

  • Dense, evenly colored red Corallium in larger sizes — uncommon in contemporary collections.
  • Dyed bamboo or sponge coral — common; frequently used in design practice and teaching sets.
  • Fossil/agatized coral with crisp rosettes — common to moderately common; favored for cabochons and display pieces.

Design & Styling Ideas 💡

Jewelry

  • Metals: Yellow/rose gold make reds and blushes glow; silver/steel cool blue/fossil neutrals.
  • Pairings: Pearls (ocean duet), black spinel/onyx (graphic pop), moonstone (soft light), turquoise (vintage Southwest vibe).
  • Shapes: Round beads = classic; tube/heishi = modern; medallion cabs = statement pendants.
  • Settings: Low‑profile bezels protect softer precious coral; fossil coral tolerates more exposure.

Home & Display

  • Fossil coral spheres/plates on matte stands—quiet, sophisticated pattern.
  • Shadowbox small carvings or cab sets on linen with minimal labels.
  • Warm, diffused lighting enhances coral’s satin glow; avoid hot spots.
Design shorthand: coral = warm, human, and slightly nostalgic. It turns outfits (and shelves) into stories.

Care & Cleaning 🧼

Do

  • Clean with lukewarm water + a drop of mild soap + soft cloth.
  • Wipe after wear—coral benefits from being free of lotions/perfume.
  • Store separately in a soft pouch; keep away from harder gems.

Don’t

  • No acids/bleach (calcite/aragonite dissolve).
  • No ultrasonic/steam, especially on dyed/stabilized pieces.
  • Avoid prolonged strong sunlight—pale tones can lighten.

Pro Tips

  • Put coral on last, take off first (after/before hairspray, perfume).
  • For vintage strands, restring periodically with knots between beads.
  • Fossil coral is quartz‑hard; routine gemstone care applies.
Quick glow saver: A 10‑second gentle wipe with a microfiber cloth restores coral’s satin sheen before photos.

Look‑Alikes & Authenticity 🕵️

Dyed Bamboo Coral

Common in teaching sets; typically shows dye in pores and at drill holes. Catalog records should note the treatment.

Sponge Coral

Open, porous texture (even when stabilized). Distinct visual character; materially different from dense precious coral.

Glass/Plastic

Too glossy, uniform color, mold lines; warm to the touch (plastic) or high luster with bubbles (glass).

Shell/Howlite Dyed “Coral”

Convincing color but different texture—look for shell growth lines or howlite’s webbing under magnification.

Fossil Coral vs. Agate

Fossil coral shows radial flowers (corallites). Regular agate shows banding/fortification instead.

At‑Home Checks

  • Loupe the surface: natural fine grain vs. plastic smoothness.
  • Check drill holes for dye pooling (bamboo/sponge).
  • Weight/feel: dense precious coral vs. feather‑light plastic.

Ethical & legal notes; related materials 🌍

Ethical & legal notes

Some coral taxa and localities are subject to national or international protections. Typical documentation records species or trade type (e.g., precious “Corallium,” bamboo, fossil), any treatments, and locality when known. Keep terminology consistent in catalog records.

Related materials used in art & design

  • Fossil/agatized coral — durable, with distinctive “flower” patterns.
  • Dyed bamboo or sponge coral — used to emulate strong red tones (record dye in notes).
  • Salmon chalcedony, carnelian, rhodochrosite — materials with coral‑adjacent palettes.
Specimen label template: “Precious coral (Corallium), trade name: ‘momo’; treatment: lightened; stabilization: none; locality: Japan (if known).”

FAQ ❓

Is coral a mineral?
No—it’s an organic gem. Precious and blue corals are mostly calcium carbonate; black coral is a proteinaceous skeleton.

Can I wear coral every day?
Yes, with mindful care. Precious/blue/black corals are softer—best in pendants, earrings, and low‑profile rings. Fossil coral is quartz‑hard and more carefree.

Why are some red corals common at lower cost?
They’re often dyed bamboo or sponge coral. Distinct materials—simply different from dense, natural‑color precious coral.

Does coral fade?
Pale tones can lighten with prolonged strong sunlight and chemicals. Store in shaded, dry places and put jewelry on after cosmetics.

What’s “angel‑skin”?
A trade term for very pale pink precious coral with a soft blush—seen in vintage pieces and modern minimal designs.

Fossil coral—really coral?
Yes. It’s ancient coral whose skeleton was replaced by silica. The “flowers” are the original colony patterns, now quartz.

Final Thoughts 💭

Coral is a quiet meeting point of ocean life and human craft. In collections and on the page, it invites close looking: growth lines in precious coral, “flower” rosettes in fossil forms, and the warm, satin way it takes a polish. Approach it with clarity—about types, treatments, and care—and it will reward you with color and history that feel both ancient and close.

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