Anthophyllite — Bladed Greens from Metamorphic Heat
Anthophyllite is an amphibole that prefers the quiet company of metamorphic rocks. It grows as bladed prisms, silky fibrous mats, and sometimes radiant sprays, wearing earthy greens and browns that feel straight from the hillside. It’s a textbook mineral for teaching cleavage angles (the classic amphibole “V”) and a subtle beauty when paired with snow‑white talc or soft grey chlorite.
Identity & Family 🔎
An amphibole with order
Anthophyllite is one of the few orthorhombic amphiboles (many cousins are monoclinic). It belongs to the anthophyllite–gedrite series, shifting chemistry by swapping Mg with Al and Fe, which nudges color from pale straw–green toward richer brown‑greens.
Name & meaning
Its name nods to “leaf‑like” aggregates—think stacks of pages or slender blades. Under the right conditions, it also grows in fine, silky fibers that form felted masses in metamorphic rocks.
Where It Forms 🧭
Metamorphosed magnesium rocks
Anthophyllite thrives where Mg‑rich rocks (like ultramafics or magnesian sediments) are cooked during regional metamorphism. It often grows alongside talc, chlorite, and orthopyroxene, marking amphibolite‑facies conditions.
Contact zones & skarns
At intrusive contacts with dolostones and Mg‑rich sediments, it can join forsterite, spinel, and cordierite in handsome skarn‑style assemblages—textbook metamorphic mosaics.
Retrograde stories
Later fluids may soften anthophyllite into talc along cleavage planes, producing a two‑tone look: hard blades framed by soft, silky alteration.
Pressure organizes the orchestra; anthophyllite plays the clarinet line—clear, woody, and beautifully directional.
Palette & Habit Vocabulary 🎨
Palette
- Pistachio to olive — Mg‑rich tones.
- Brown‑green — Fe‑richer or weathered blades.
- Pearly silver — on fresh cleavage and fibrous sheens.
- Grey — common in massive aggregates.
Luster is vitreous on fresh faces, pearly–silky on fibrous surfaces; edges can show a subtle satiny glow.
Habit words
- Bladed/prismatic — elongated crystals with crisp terminations.
- Radiating sprays — starburst clusters from a central point.
- Fibrous — felted mats or veinlets of fine fibers.
- Granular/massive — interlocking amphibole mosaics in schists.
Photo tip: Low, raking light makes cleavage planes flash; a matte dark plinth keeps olive tones from washing out.
Physical & Optical Details 🧪
| Property | Typical Range / Note |
|---|---|
| Chemistry | Mg₇Si₈O₂₂(OH)₂ with Fe substitution to ferroanthophyllite; Al‑rich trend toward gedrite |
| Crystal system / Group | Orthorhombic amphibole |
| Hardness (Mohs) | ~5.5–6 |
| Specific gravity | ~2.9–3.2 (rises with Fe) |
| Cleavage / Fracture | Two good cleavages at ~56° & 124°; fracture splintery–uneven |
| Luster / Transparency | Vitreous to pearly; translucent on thin edges, otherwise opaque |
| Optics | Biaxial (+); RI ~1.61–1.66; birefringence up to ~0.02; pleochroism pale straw→olive→brown |
| Streak | White |
| Alteration | Common to talc, chlorite, serpentine along cleavage & rims |
| Treatments | None typical; polished slabs are uncommon due to splintery fracture |
Under the Loupe 🔬
Cleavage “V”
Two intersecting cleavage sets meet near 56° and 124°. On broken ends, they form a neat, repeated V—very satisfying to spot.
Splintery ends
Fresh breaks look splintery with tiny spear‑like shards. Edges often show pearly flashes under side light.
Alteration halos
Look for talc or chlorite along cracks—a pale rim that softens the outline and adds texture contrast.
Look‑Alikes & Mix‑ups 🕵️
Hornblende (common amphibole)
Often darker and monoclinic; chemistry is Ca‑bearing. Cleavage angles are similar, but hornblende rarely shows the orthorhombic, bladed look of anthophyllite sprays.
Tremolite–actinolite
Whiter to grass‑green amphiboles; typically more fibrous and Ca‑rich. Thin edges of tremolite can be nearly colorless.
Orthopyroxene (enstatite)
Two cleavages near 90° (pyroxene style), not the amphibole V. Often more bronzy and has different luster.
Cummingtonite–grunerite
Monoclinic amphiboles with brown tones; optical tests or detailed habit comparisons help separate them from anthophyllite.
Quick checklist
- Olive–brown blades or sprays?
- Distinct cleavage V at ~56°/124°?
- Pearly edges; talc/chlorite fringes? → Anthophyllite.
Localities & Notes 📍
Where it shines
Classic metamorphic belts in Scandinavia (Norway, Finland), the Appalachians (USA), and parts of the Alps and India produce handsome bladed clusters and felted aggregates with talc and chlorite.
How people use it
As a collector mineral and a metamorphic indicator—its presence helps geologists read pressure–temperature histories. Lapidary uses are rare due to splintery fracture.
Care & Display 🧼⛰️
Handling
- Support from beneath; anthophyllite can be splintery along cleavage.
- Use a puffer or very soft brush; avoid vigorous rubbing that lifts tiny shards.
- Keep away from gritty surfaces that could scratch pearly faces.
Mounting & storage
- Seat on foam or acrylic cradles; secure gently at the base.
- For very fine fibrous pieces, display under a clear cover to keep surfaces undisturbed.
- Transport snugly so blade tips don’t rattle.
Photography
- Low, directional light to ignite the pearly sheen.
- Black flags tame hotspots; a pale side reflector opens shadows between blades.
- Angle to show the cleavage V—it’s the amphibole signature.
Hands‑On Demos 🔍
Cleavage compass
Shine a narrow beam along a broken edge and trace the two gleaming planes—measure the angle (you’ll land near 56°/124°). It’s a mini structural‑geology lesson.
Alteration contrast
Under a loupe, find pale talc or green chlorite rims along anthophyllite blades. The texture change tells a cooling‑fluids story in millimeters.
Anthophyllite is mountain building in miniature—orderly, directional, and quietly strong.
Questions ❓
Why orthorhombic matters?
It sets anthophyllite apart from most amphiboles (often monoclinic). The symmetry shows up as crisp, bladed habits and specific optical behavior.
Is it always green?
No—Mg‑rich pieces look pale straw to olive; Fe‑rich ferroanthophyllite trends brown‑green. Weathering and alteration add grey and pearly tones.
Can it be cabbed?
Rarely. The splintery fracture and cleavage make cutting tricky. Collectors prefer natural clusters and matrix pieces.
What’s with anthophyllite–gedrite?
They’re a solid‑solution series. As Al increases (gedrite side), colors deepen and some properties shift subtly; many specimens plot between the endmembers.