Labradorite

Labradorite

Crystal system · Triclinic

Labradorite is a silicate mineral prized by collectors for its exceptional color range, with notable Chinese occurrences.

About Labradoriteextended article

Crystal Structure

Intermediate plagioclase showing exsolution lamellae.

Elemental Composition (by mass)

Element	Mass %	Visual
O Oxygen	48.81%
Si Silicon	32.13%
Al Aluminum	10.29%
Na Sodium	8.77%

Computed from simplified end-member formula. Solid-solution series, water content, and trace substitutions cause real-world variation.

IMA Abbreviation (Whitney-Evans 2010)

Lab

→ Labradorite

Intermediate plagioclase

Standard symbol from American Mineralogist (Whitney & Evans, 2010). Used in thin-section labeling, phase diagrams, and IMA-style species records.

Pronunciation

/ˈlæbrədɔːraɪt/

↔ LAB-ruh-dor-ite

from Labrador

Tenacity

Behavior:

brittle

Under stress:

Cleaves

Plagioclase.

Luster

vitreous→iridescent

Labradorescence is a separate phenomenon from base luster.

Color Cause (Chromophore)

Chromophore:

lamellar interference

Mechanism:

physical optical effect

Color produced:

iridescent

Body color often gray; labradorescence from thin albite-anorthite exsolution lamellae.

Diaphaneity (Transparency)

translucent

Schiller layers create labradorescence.

Type Locality

Paul Island, Labrador — Canada

Described 1770 by Werner

› Browse all type localities

Specific Gravity

2.68–2.72

g/cm³

light

Intermediate plagioclase; labradorescence.

For comparison: water = 1.00, glass ≈ 2.5, quartz = 2.65, corundum ≈ 4.00, galena ≈ 7.50, gold ≈ 19.3.

Twinning Laws

Albite lawlamellar

Polysynthetic twin lamellae produce the optical conditions for labradorescence.

Cleavage & Fracture

Cleavage:

good 2 directions ~86°

Fracture:

uneven

Albite-law twinning produces fine striations.

Market availability: Uncommon

Found at major shows and select dealers. Quality varies by locality.

Collector tier: Cabinet Classic

World-class display species — sought after for cabinet collections, well-documented localities, frequent show-piece pieces.

Mohs 6–6.5

Vickers (~) 820 HV

Knoop (~) 870 HK

Nickel–Strunz 9.FA.35

Dana 76.01.03.06

Element composition by mass

Formula: (Ca,Na)(Al,Si)₄O₈ · molar mass: 269.66 g/mol

O	47.46%
Si	20.83%
Al	20.01%
Ca	7.43%
Na	4.26%

Computed from atomic weights (IUPAC 2021). Site-occupancy groups (Fe,Mn) split equally.

GroupFeldspar Group

Related members: Orthoclase · Microcline · Sanidine · Albite

Optical Effects

Labradorescence

Mohs Hardness 6–6.5

1
Talc 2
Gypsum 3
Calcite 4
Fluorite 5
Apatite 6
Orthoclase 7
Quartz 8
Topaz 9
Corundum 10
Diamond

Labradorite sits at 6–6.5 on the Mohs scale — just hard enough to scratch glass.

Colors:

Streak
White

Crystal system
Triclinic

Pronunciation/ˈlæbrədərˌaɪt/

Type localityTabor Island, Labrador, Newfoundland and Labrador, Canada (1770)

SilicatesSilicates (Tectosilicates — Feldspars)

TL;DR · 1 min read

Labradorite (Ca,Na)(Al,Si)₄O₈ is a calcium-rich plagioclase feldspar famous for its iridescent labradorescence — a vivid blue, green, gold, and purple flash from light interference within microscopic exsolution lamellae. Discovered in 1770 in Labrador, Canada, and now sourced primarily from Madagascar (Tulear) and Finland (spectrolite variety).

More minerals to explore

About Labradorite

Labradorite belongs to the silicate class in the plagioclase feldspar group and has the chemical formula (Ca,Na)[Al(Al,Si)Si2O8]. It crystallizes in the triclinic system and is one of the most visually varied minerals in the collector market. Its combination of structural character and global distribution make it a recognized species in both systematic and aesthetic collections.

Identification & care

Crystals commonly develop as tabular, massive; rare distinct crystals; polysynthetic twinning (albite law and pericline law produce characteristic striations). Its color range is broad, including grey, white, dark grey, labradorescence: spectral blue, green, gold, orange, red, and violet iridescence on cleavage planes. The luster is vitreous, sub-vitreous, the streak is white, and specimens range from translucent to opaque. The cleavage is perfect on {001}, good on {010} — feldspar cleavage. The fracture is uneven, conchoidal, which aids identification.

Collector context

How it forms

In terms of geology, Labradorite forms in intermediate to mafic igneous rocks (anorthosite, gabbro, norite, basalt); some metamorphic rocks; widespread rock-forming mineral. It is commonly found in association with pyroxene (augite), olivine, ilmenite, magnetite, hypersthene, hornblende.

Classic Chinese localities

Documented Chinese occurrences are recorded at Bayan Obo deposit, among others.

Why collectors care

Collectors pursue Labradorite for the clarity of its crystal form and, in good material, saturated color that reads instantly across a display case. A well-terminated labradorite on clean matrix photographs well, identifies quickly, and anchors a cabinet piece. Top Chinese specimens over the last two decades have reset the bar for what labradorite looks like at collector grade.

What affects value

Value in Labradorite is assessed, in typical order of weight, against: (1) locality provenance; (2) size relative to the species norm; (3) crystal form and termination sharpness; (4) color saturation and zoning; (5) transparency and internal clarity; (6) matrix quality and aesthetic balance; (7) condition (absence of damage, chips, or repair). Cleaning quality and verified locality documentation act as multipliers across the above.

Naming history

The name Labradorite has a specific etymological and historical context — see Mindat's reference entry for provenance details. We have retained naming data at the record level; published prose is paraphrased from factual fields rather than copied from source.