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Larimar

Larimar • Blue Pectolite (NaCa2Si3O8(OH)) Crystal System: Triclinic • Biaxial (–) Mohs ~4.5–5 • SG ~2.8–2.9 Habit: Fibrous–radiating masses & spherulites Locality: Dominican Republic (Barahona)

Larimar — Caribbean Sky, Written in Stone

Larimar is the sea‑blue variety of the mineral pectolite, found essentially in one place on Earth: the mountains of the southwestern Dominican Republic. Its palette runs from cloud‑white through soft “shoreline” blues to deep volcanic turquoise, patterned with feathery, fibrous networks. Tilt a polished piece and the light skims across silky structures—like sunlight rippling through shallow water. (No sunscreen required.)

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Color Mechanism
Cu2+ substituting in pectolite → blue tones
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Texture
Fibrous, radiating aggregates; silky luster
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Geologic Setting
Hydrothermal veins in basalt/andesite

Identity & Naming 🔎

What it is

Larimar is a blue variety of pectolite, a calcium‑sodium inosilicate with the formula NaCa2Si3O8(OH). Pectolite typically grows as fine, silky fibers that radiate from centers; when these aggregates are compact and take a high polish, we get the gem material collectors call Larimar.

Where the name came from

The name “Larimar” blends Lari‑ (for Larissa, the discoverer’s daughter) and ‑mar (Spanish for “sea”), a nod to both family and the stone’s oceanic colors. You may also see “Atlantis stone” or “Stefilia’s stone” in older references; the mineralogical name is still pectolite.

Color note: The blue is widely attributed to small amounts of copper in the lattice, sometimes with subtle variations that shift tones from sky to green‑blue.

Formation & Geological Setting 🌍

Volcanic backdrop

Larimar forms in the amygdaloidal and vein systems of altered basalts and andesites. After the lavas cooled and fractured, hot fluids rich in silica and alkalis moved through, depositing pectolite along cracks and cavities.

Hydrothermal chemistry

As fluids interacted with the host rocks, calcium and sodium combined with silica to build the pectolite structure. Trace copper likely substituted for calcium in small amounts, tinting the otherwise white mineral blue.

From mountains to rivers

Primary material occurs in veins (notably at Los Chupaderos near Barahona). Weathering then frees nuggets that roll into streams; early finds were made as smooth blue pebbles along riverbeds.

Geology haiku: lava cools, cracks breathe; hot waters paint the fissures—sky pools in stone.

Appearance & Patterns 👀

Palette

  • Cloud white — fibrous meshes and starbursts.
  • Sky blue — translucent pools between white fibers.
  • Caribbean blue — saturated, almost electric zones.
  • Green‑blue — copper‑leaning variations, sometimes near veins.
  • Rusty brown — hematite or iron staining at margins.

Textures & scenes

  • Radiating fans and spherulites that look like sea anemones under a loupe.
  • Spider‑webbing of silky white fibers that frame blue “lagoons.”
  • Occasional chatoyant silk along aligned fibers—a soft, linear sheen.

Photo trick: Side‑light at ~30° reveals the silky fabric; a white bounce card opposite the light evens the blue without glare.

Physical & Optical Properties 🧪

Property Typical Range / Note
Chemistry NaCa2Si3O8(OH) (pectolite); blue tones from minor Cu
Crystal system Triclinic; aggregates are fibrous to radial
Hardness ~4.5–5 (softer than quartz; takes a high polish with care)
Specific gravity ~2.8–2.9
Cleavage / Fracture Perfect to good cleavage in more than one direction; splintery fracture in fibrous material
Refractive indices nα ≈ 1.595–1.610 • nβ ≈ 1.614–1.631 • nγ ≈ 1.631–1.645
Birefringence ~0.030–0.040 • Optic sign (–)
Luster Silky to vitreous on polished faces
Transparency Opaque to translucent in thin blue zones
Common associates Calcite, zeolites (e.g., natrolite), prehnite, hematite
Working caution: The fibrous habit can produce needle‑like splinters on breaks. For lapidary work, use dust control and avoid aggressive pressure—let the abrasives do the job.

Under the Loupe / Microscope 🔬

Radiating fabrics

10× magnification reveals radial fiber bundles that intersect like reefs and tide pools. Boundaries between bundles often outline the blue patches.

Inclusions & veins

Thin calcite or zeolite veins may thread the stone; iron oxides add warm freckles. Rarely, micro‑cavities host tiny drusy crystals.

Surface hints

Polished larimar shows a silky gloss rather than glassy glare, especially where fibers are aligned. Subtle linear sheen can mimic a soft cat’s‑eye when cut en cabochon along fiber directions.

Look‑Alikes & How to Tell 🕵️

Turquoise

Usually more uniform robin’s‑egg blue with black/brown matrix; different chemistry (copper aluminum phosphate) and waxy luster. Turquoise lacks larimar’s silky, fibrous fabric under a loupe.

Chrysocolla

Blue‑green copper silicate; often mottled with malachite and quartz. Texture tends botryoidal or chalcedonic, not radiating fibrous fans.

Amazonite (microcline feldspar)

Green‑blue with grid‑like cleavage and perthitic streaks; higher hardness and distinct feldspar blockiness—no silky radial structures.

Blue calcite

Softer (Mohs 3), rhombohedral cleavage; blue is more transluscent and even, without fibrous webs. A fingernail won’t scratch larimar but can mark calcite.

Dyed howlite/magnesite

Color pools in pores and drill holes; “neon” blues are a red flag. Under magnification, you’ll see dye halos rather than natural fiber networks.

Quick checklist

  • Silky, radiating fibrous texture framing the blues.
  • Soft‑to‑medium hardness (4.5–5) with high polish.
  • Dominican locality strongly suggests larimar.

Localities 📍

Dominican Republic (Barahona)

The type and principal locality for larimar. Veins in altered basalts near Los Chupaderos yield compact, gemmy pectolite with the signature Caribbean palette. Stream‑worn pebbles occur in nearby drainages.

Elsewhere?

White‑to‑gray pectolite is widespread globally, but the vivid blue variety with this particular look is essentially unique to the Dominican Republic.

Care & Stability 🧼

Everyday handling

  • Hardness is moderate; avoid hard knocks and sharp edges.
  • Polish holds well if stored separately from quartz and corundum neighbors.

Cleaning

  • Use lukewarm water, mild soap, and a soft cloth; rinse and dry.
  • Avoid ultrasonic/steam cleaners and avoid acids or ammonia.

Display notes

  • Normal indoor light is fine. Prolonged high heat is unkind to many calc‑silicates—treat like a warm‑weather friend, not a sunbather.
  • Side‑lighting highlights the silky fabric; back‑lighting can reveal translucent blue margins.
Lapidary aside: Use fresh abrasives, light pressure, and plenty of coolant. Fibrous splinters can be sharp—dust control and gloves are your buddies.

Questions ❓

Is larimar the same as pectolite?
Larimar is pectolite—specifically the blue, compact variety that takes a good polish. White or gray pectolite is common, but the blue is distinctive and locality‑tied.

Why do some pieces look greener?
Small shifts in chemistry and microscopic inclusions can nudge tones toward green‑blue, especially near veins or alteration zones.

Does the color fade?
Larimar’s color is generally stable in normal conditions. Heat and harsh chemicals are the main things to avoid.

Are treatments common?
Most quality pieces are natural apart from cutting and polishing. Lower‑grade material may be stabilized with resins; look for clear disclosure and check drill holes/edges for tell‑tale resin sheen.

What makes a visually striking piece?
Balanced contrast between vivid blue pools and crisp white fibers, with minimal brown staining and a clean, even polish. A little silky sheen along fibers is a delightful bonus.

Small joke to close: it’s called Larimar because “office‑fluorescent‑light‑blue” didn’t inspire anyone to go rock hunting.
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