Sugilite

Sugilite

Sugilite • cyclosilicate (milarite‑group) — idealized KNa₂(Fe,Mn,Al)₂Li₃Si₁₂O₃₀ Crystal system: Hexagonal • Habit: massive, granular; rare microcrystals Mohs: ~6–6.5 • SG: ~2.74–2.80 • Luster: vitreous to waxy Colors: lavender → royal purple; translucent “gel sugilite” exists Also seen as: lavulite (older trade name)

Sugilite — Royal Purple Written in Stone

Sugilite is the grape‑jelly purple that lapidaries dream about—sometimes opaque and graphic, sometimes a juicy, translucent “gel.” Chemically it’s a ring‑silicate in the milarite family; historically it’s a globe‑trotting story from a Japanese island outcrop to South Africa’s Kalahari Manganese Field. One glance and you’ll understand why collectors call it “royal.” (No actual crowns included—just very regal color.)

🔬
What it is
Purple cyclosilicate with rings of SiO₄ tetrahedra; chemistry varies with Fe/Mn/Al/Li content—hence shades from lilac to deep violet
🎨
Why it captivates
A royal, saturated purple seldom seen in other opaque stones; silky mottling, black manganese “ink” lines, and rare translucent gel pieces that glow
🧼
Care snapshot
Mohs 6–6.5; avoid harsh acids/ultrasonics/steam; mild soap + water, soft cloth; store separate from quartz & corundum

Identity & Naming 🔎

A ring‑silicate with star credentials

Sugilite belongs to the milarite group of cyclosilicates (silicate rings). It’s usually hexagonal and forms massive to granular aggregates rather than showy crystals—perfect for cabochons and inlay.

What’s in a name?

Named for Japanese petrologist Ken‑ichi Sugi, who studied early occurrences in Japan. The gem world only took notice after rich South African finds brought royal purple to the lapidary bench.

Trade tip: You may see the older name lavulite attached to vivid South African material; it’s all sugilite—just a vintage label.

Where It Forms 🧭

Kalahari chemistry

The most celebrated sugilite comes from the Wessels & N’Chwaning mines of the Kalahari Manganese Field (South Africa). There, sodium‑rich fluids percolated through Mn‑rich rocks, crystallizing sugilite alongside aegirine, richterite, bustamite, and Mn‑calcite.

Island beginnings

Earlier occurrences were described from Japan (Iwagi Islet, Ehime Prefecture) as tiny crystals in aegirine‑bearing syenite—scientifically important, gemologically modest.

From massive to “gel”

Geologic conditions and trace chemistry control translucency: opaque massive material (most common) vs. rare translucent “gel” sugilite with glowing wine‑purple depth.

Sugilite is a team player—manganese sets the stage, sodium and lithium cue the color, and time does the polishing.

Palette & Pattern Vocabulary 🎨

Palette

  • Royal violet — classic South African look.
  • Lavender — lighter, often more mottled.
  • Wine‑purple “gel” — translucent slabs/cabs.
  • Ink‑black — manganese oxide/aegirine seams.
  • Bone/grey — feldspathic or calcite host patches.

Finish ranges from waxy to vitreous. Translucent areas take a lush, glassy polish that looks lit from within.

Pattern words

  • Mottle — soft clouds of lighter/darker purple.
  • Net veining — black Mn‑oxide lines “inking” the purple field.
  • Streaks & strands — slender aegirine needles or dark stringers.
  • Gel windows — translucent panes within otherwise opaque mass.

Photo tip: Use a broad, soft key light to hold saturated purple; a small side kicker crisps the black veining. Backlight thin “gel” pieces for a stained‑glass moment.

Physical & Optical Details 🧪

Property Typical Range / Note
Chemistry KNa₂(Fe,Mn,Al)₂Li₃Si₁₂O₃₀ (Fe/Mn/Al ratios vary; Li is essential)
Crystal system / Group Hexagonal • Cyclo‑silicate (milarite group)
Hardness (Mohs) ~6–6.5 (good daily‑wear with care)
Specific gravity ~2.74–2.80
Refractive index / Optics ~1.607–1.614; birefringence ~0.002–0.004; uniaxial (−)
Pleochroism Weak–moderate: violet ↔ slightly red‑violet in translucent pieces
Luster / Transparency Waxy–vitreous; opaque to translucent (rarely near‑transparent)
Cleavage / Fracture Poor/indistinct cleavage; uneven to subconchoidal fracture; brittle
Fluorescence Weak to none (some stones show dull red/orange due to Mn‑bearing associates)
Treatments Possible dyeing to intensify purple; stabilization/impregnation for porous areas; “reconstituted” resin composites exist—request disclosure
Plain‑English ID: saturated purple with black Mn “ink,” waxy‑to‑glassy polish, SG under 3, and a calm RI near 1.61—distinct from quartz (1.54) and jade (≈1.66–1.67).

Under the Loupe 🔬

Purple micro‑mosaic

Massive sugilite shows a granular fabric of interlocking purple domains with soft boundaries; cleaner “gel” zones appear smoother and transmit light.

Dark companions

Look for aegirine as slender black needles, manganese oxides as inky seams, and calcite as pale veins—common in Kalahari material.

Treatment clues

Dyed stones can show color pooling in pores and drill holes; resin‑rich areas have a plasticky glare and lower heft. Natural pieces keep subtle mottling and a mineral sheen.

Look‑Alikes & Imitations 🕵️

Charoite

Also purple, but with dramatic chatoyant swirls and silky fibrous texture; typically higher RI and different associations (syenite of Siberia).

Amethyst (quartz)

Transparent with crystal facets and RI ~1.54; no black Mn veining; very different feel in hand and under light.

Lepidolite & purple mica

Flaky/cleavable with micaceous sparkle; softer to the nail and lower toughness.

Dyed howlite/magnesite

Porous, often too‑even purple; color concentrates in pits and around holes; hardness ~3.5–4 (scratches easily).

“Purple jade” mislabels

Nephrite/jadeite rarely reach sugilite purple; RI/SG and texture separate them quickly in the lab.

Quick checklist

  • Bold, royal purple with black Mn lines?
  • RI ~1.61, SG ~2.75, no mica sheen?
  • Translucent “gel” windows (sometimes)? → Likely sugilite.

Localities & Uses 📍

Where it shines

South Africa (Kalahari Manganese Field) is the benchmark for gemmy purple, including rare translucent material. Additional occurrences include Japan (type locality, microcrystalline), and reports from Canada, Italy, and elsewhere—usually minor in gem terms.

What people make

Cabochons and beads that showcase mottled violet fields, inlay for bold color accents, and the coveted “gel sugilite” cabs that look like poured wine glass—responsible for many happy gasps at gem shows.

Labeling idea: “Sugilite — cyclosilicate (milarite group) — purple, opaque/translucent — treatment (none/dyed/stabilized) — locality.” Clear and collector‑friendly.

Care, Jewelry & Lapidary 🧼💎

Everyday care

  • Clean with lukewarm water + mild soap; soft cloth dry.
  • Avoid ultrasonics, steam, and strong chemicals (especially if veined or stabilized).
  • Store separately—quartz and corundum can scuff the polish.

Jewelry guidance

  • Excellent for pendants, earrings, brooches.
  • For rings, choose protective bezels or low‑profile designs.
  • Translucent “gel” pieces benefit from clean backs and closed settings to deepen color.

On the wheel

  • Inspect for Mn‑oxide seams; stabilize if needed & disclose.
  • Cab with light pressure; pre‑polish 600→1200→3k; finish with alumina or cerium oxide on leather/felt.
  • Keep cool—heat can encourage micro‑cracking along dark veins.
Display tip: Pair one opaque cab with a thin backlit slice of “gel” sugilite—same chemistry, two moods. It’s a crowd‑pleaser.

Hands‑On Demos 🔍

Pleochroism peek

With a dichroscope on a translucent piece, look for two violet shades that trade places as you rotate—subtle but satisfying.

Matrix map

Under 10×, trace a black seam and find an aegirine needle or calcite vein crossing the purple field. It turns the stone into a tiny geologic map.

If purple had a passport, it would stamp “Japan” and “Kalahari,” then settle into a pendant with a contented glow.

Questions ❓

Why do some pieces look patchy?
Natural mottling reflects variable Fe/Mn content and intergrowth with dark Mn minerals—part of sugilite’s signature.

Does sugilite fade?
Color is generally stable indoors. Avoid prolonged high heat or harsh chemicals that can haze polish or affect treated stones.

How common is “gel sugilite”?
Rare. Most material is opaque; translucent, clean purple is much scarcer and prized accordingly.

How to spot imitations?
Watch for too‑even purple, dye in pores/holes, resin‑heavy feel, and very low hardness. A gem lab can confirm with RI/SG and spectroscopy.

Back to blog