Eskolaite is a rare chromium oxide mineral known for its distinct deep emerald green color and high hardness. It is typically found as small, opaque crystals within metamorphic rocks like skarns or as granular masses associated with other chromium-bearing minerals.
Is this eskolaite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch eskolaite with a known reference. Eskolaite sits at Mohs 8, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale green.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: black, dark green.
- 5Look at form & habitCrystal system: trigonal. Typical habit: hexagonal, platy, prismatic.
Often confused with
Eskolaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Eskolaite is noticeably harder (Mohs 8 vs. 5-6); streak differs, so Eskolaite leaves pale green, Hematite leaves cherry-red or reddish brown; luster reads vitreous on Eskolaite and metallic or submetallic to dull on Hematite.
How to tell apart: Eskolaite is noticeably harder (Mohs 8 vs. 5-6); streak differs, so Eskolaite leaves pale green, Ilmenite leaves black to reddish brown; luster reads vitreous on Eskolaite and metallic to submetallic on Ilmenite.
How to tell apart: Corundum is the harder of the two (Mohs 9 vs. 8); streak differs, so Eskolaite leaves pale green, Corundum leaves white; luster reads vitreous on Eskolaite and adamantine to vitreous; pearly on partings on Corundum.
Often found alongside eskolaite
Minerals reported to co-occur with eskolaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cr₂O₃
- Mohs hardness
- 8
- Density
- 5.18 g/cm³
- Colors
- Streak
- Pale green
- Luster
- Vitreous
- Transparency
- Opaque, translucent in thin edges
- Crystal system
- Trigonal
- Crystal habit
- Hexagonal, platy, prismatic
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- In chromium-rich tremolite skarns, metaquartzites, and chlorite veins (Outokumpu, Finland); on greywacke pebbles in a glacial boulder clay deposit (Callowhill Upper, Ireland)
Where rockhounds find eskolaite
Classic worldwide localities
- Outokumpu, Finland
- Nizhni Tagil, Ural Mountains, and on the western shore of Lake Baikal, 4.5 km south of Olkhon Gate Strait, Siberia, Russia
- Found near Dukou, Szechwan Province, China
- Callowhill Upper, near Newtown Mt. Kennedy, Co. Wicklow, Ireland
- Chapada Diamantina, Bahia, Brazil
- Merume River and its tributaries, Mazaruni district, Guyana
Field-hunting tip
Where it forms: In chromium-rich tremolite skarns, metaquartzites, and chlorite veins (Outokumpu, Finland); on greywacke pebbles in a glacial boulder clay deposit (Callowhill Upper, Ireland). If you start seeing guyanaite, pyrrhotite, pentlandite in float, you are in the right ground. Typical habit: hexagonal, platy, prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
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Find eskolaite on the map
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