Nuummite

Nuummite

Nuummite • metamorphic rock rich in amphiboles (gedrite & anthophyllite) Signature: shimmering schiller from ultra‑thin metallic lamellae (ilmenite/magnetite) Mohs: ~5.5–6 • SG: ~2.9–3.2 • Luster: sub‑vitreous; silky when fibrous Look: black base with bronze–gold (often blue/green) iridescent blades Type locality: Nuuk (Nuussuaq/“Nuummit”), southwest Greenland

Nuummite — Night‑Black Stone with Ancient Fire

Nuummite is a dark, fine‑grained metamorphic rock that looks like night sky sprinkled with embers. Rotate it and thin metallic lamellae flare gold, bronze, sometimes peacock blue—little lightning strikes trapped in stone. It’s composed mainly of amphiboles (gedrite and anthophyllite), forged under heat and pressure, and made famous by its home near Nuuk in Greenland. In short: a quiet stone until the light hits—then it tells stories. (No campfire needed.)

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What it is
A rock (not a single mineral): amphibole‑dominant with fine exsolution lamellae of opaque oxides that create iridescent schiller
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Where it forms
High‑grade metamorphism of mafic/ultramafic rocks; recrystallization aligns blade‑like amphiboles that later host metallic lamellae
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Care snapshot
Moderately hard with cleavage; avoid hard knocks, ultrasonics & steam; mild soap + water; store away from quartz/corundum neighbors

Identity & Naming 🔎

A Greenland original

Nuummite takes its name from the Nuuk region of Greenland, where classic material was described from dark amphibole rocks shot through with shimmering metallic blades. The name has since become shorthand for this distinctive look: black base + bronze/blue flashes.

Rock, not species

Because nuummite is a rock, properties vary. The stars of the assemblage are gedrite and anthophyllite (amphiboles); minor biotite, quartz, and opaque oxides (ilmenite/magnetite) add the showy optics.

Name hygiene: you’ll see “Chinese nuummite” and other trade names for dark, flashy amphibole gneisses. Beautiful in their own right, but true Greenlandic nuummite is its own classic.

How It Forms 🧭

Metamorphic forge

Starting from mafic/ultramafic protoliths, heat + pressure transform the rock into amphibole‑rich layers. Amphiboles grow as elongated blades that tend to align—nature’s fiber optics laid down in stone.

Metallic lamellae

During cooling, ultra‑thin exsolution lamellae of iron‑titanium oxides can form within those blades. Their nanoscale spacing interferes with light, creating iridescent schiller—most often bronze/gold, sometimes blue/green.

Why it “turns on”

The flash is directional. When lamellae and light align, colors ignite; a small tilt can make blades go from quiet to blazing. Cutters orient slabs to maximize that effect face‑up.

Recipe: amphibole blades + ultra‑thin metallic films + a good tilt toward the light = the nuummite glow.

Palette & Pattern Vocabulary 🎨

Palette

  • Inky black base — fine‑grained amphibole matrix.
  • Bronze/gold flames — hallmark lamellae flashes.
  • Peacock blue/green — less common, striking when present.
  • Smoke graphite — non‑flash areas with subtle sheen.

Good material looks almost holographic: blades light up and fade as you move.

Pattern words

  • Feather flames — bundles of parallel flashes like brush‑strokes.
  • Cross‑fire — intersecting blade sets form X‑shaped gleams.
  • Window panes — rectangular flashes from blocky sections.
  • Galaxy scatter — small, starry points of bronze in a dark field.

Photo tip: Use a small, movable point light at ~25–35°. Sweep slowly—stop where the blades blaze, then add a soft fill to keep the black base rich.

Physical & Optical Details 🧪

Property Typical Range / Note
Composition Amphibole rock (dominantly gedrite + anthophyllite) with minor quartz, biotite, and opaque oxides
Hardness (Mohs) ~5.5–6 (sturdy but not quartz‑hard)
Specific gravity ~2.9–3.2 (varies with oxide content)
Cleavage Amphibole cleavage (~56°/124°); slabs can part if edges are thin across cleavage
Luster Sub‑vitreous to silky; metallic schiller from ultra‑thin lamellae
Optics Complex (polymineralic); iridescence is a thin‑film/diffraction effect—strongly directional
Magnetic response Often weakly attracted to a strong magnet (magnetite lamellae)
Treatments Typically untreated; occasional surface wax/resin for luster; composite backings for large thin cabs
Everyday translation: it’s tough enough for jewelry but appreciates protective settings and a little personal space in storage.

Under the Loupe 🔬

Blade anatomy

At 10× you’ll see parallel amphibole blades with ultra‑thin, reflective films along them. Rotate the light—colors surge and vanish in those films.

Metallic lamellae

Ilmenite/magnetite lamellae appear as dark, mirror‑bright lines or plates. Their spacing controls color: tighter spacing → cooler tones; slightly wider → bronze/gold.

Texture & associates

Fine quartz/biotite intergrowths are common. Along cleavage, you may spot tiny step‑downs; edges benefit from micro‑bevels to discourage flaking.

Look‑Alikes & Mix‑ups 🕵️

Labradorite / spectrolite

Feldspar with labradorescence—broad color panels, not fine metallic blades. Feldspar is lighter (SG ~2.7) and shows different cleavage & feel.

Hypersthene / bronzite

Orthopyroxenes with silky schiller and bronze sheen; typically show fibrous cat’s‑eye‑like highlights rather than discrete metallic lamellae.

“Chinese nuummite”

Dark amphibole gneiss (often arfvedsonite‑rich) with blue/green flash. Gorgeous—but different texture under the loupe and different mineral makeup.

Astrophyllite‑bearing rocks

Show bronze starry blades in lighter matrices; usually far more micaceous/stellate and lack nuummite’s inky base.

Glass with foil

Uniform weight/feel, bubbles, and trapped foils betray man‑made pieces. Nuummite’s flashes live within mineral blades, not as inserted sheets.

Quick checklist

  • Black base with fine metallic blades that switch on/off?
  • Weak magnet tug on a neodymium magnet?
  • Amphibole cleavage hints on edges? → Nuummite likely.

Localities & Notes 📍

Where it shines

The classic source is the Nuuk (Nuussuaq) area of Greenland, where amphibole rocks with brilliant bronze/blue flashes became the archetype. Dark, flashy amphibole rocks from other regions exist, but the Greenland look—inky base, crisp metallic flames—sets the standard.

How it’s cut

Cutters orient slabs so blade sets run parallel to the dome face. That orientation produces broad, face‑up flashes instead of edge‑only streaks—exactly what you want in cabochons and freeforms.

Labeling idea: “Nuummite (amphibole rock: gedrite/anthophyllite) — black with bronze/blue schiller — locality.” Short, accurate, collector‑friendly.

Care & Lapidary Notes 🧼💎

Everyday care

  • Clean with lukewarm water + mild soap; soft cloth; dry promptly.
  • Avoid ultrasonics/steam and harsh chemicals.
  • Store separately; quartz/corundum neighbors can haze edges over time.

Jewelry guidance

  • Great for pendants, earrings, statement rings. Use protective bezels or frames—remember amphibole cleavage.
  • Open backs lighten the look; brushed silver or blackened metals intensify the ember‑glow.
  • Reserve everyday knock‑about wear for sturdier gems; nuummite is best as mindful‑wear jewelry.

On the wheel

  • Orient to put the brightest blade set face‑parallel; test with a flashlight before committing the cut.
  • Light pressure; pre‑polish 600→1200→3k; finish with alumina or cerium on a firm pad.
  • Micro‑bevel girdles; avoid thin, unsupported corners across cleavage.
Display tip: A small, low‑angle spotlight beside a matte black plinth makes the blades leap alive—like sparks in a dark room.

Hands‑On Demos 🔍

Find the “on switch”

Hold a point light and rotate the stone. When the blades ignite, mark that direction—it’s the best face‑up orientation for setting or display.

Magnet whisper

Place a strong neodymium magnet near a loose cab on a very low‑friction surface. A slight nudge betrays magnetite lamellae—geologic Easter egg!

Small joke: nuummite is the introvert of flashy stones—it only performs when the lighting is just right.

Questions ❓

Is nuummite a single mineral?
No—nuummite is a rock, typically dominated by amphiboles (gedrite/anthophyllite) with thin metallic lamellae that create the flash.

Why does it look different from piece to piece?
The density, thickness, and orientation of lamellae vary, changing color and intensity. Orientation during cutting matters a lot.

Does it always show blue?
Bronze/gold is most common. Blue/green requires particular lamella spacing and lighting—rare but coveted.

Good for daily wear rings?
With protective settings and mindful wear. It’s moderately hard but has amphibole cleavages; pendants/earrings are carefree winners.

How do I tell it from labradorite?
Labradorite shows broad, pane‑like color fields in a lighter feldspar body. Nuummite shows fine metallic blades lighting up in a deep black base.

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