Pumpellyite-(Mg) is a sorosilicate mineral frequently found as a secondary mineral in altered igneous rocks. It is most recognized for its distinct radiating or fibrous habit in shades of green and blue-green, often forming within veins or amygdules.
Is this pumpellyite-(mg)?
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 pumpellyite-(mg) with a known reference. Pumpellyite-(Mg) sits at Mohs 5.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: blue green, olive green, brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous, massive, spherical.
Often confused with
Pumpellyite-(Mg) vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside pumpellyite-(mg)
Minerals reported to co-occur with pumpellyite-(mg). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂MgAl₂(SiO₄)(Si₂O₇)(OH)₂·H₂O
- Mohs hardness
- 5.5
- Density
- 3.18 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent to nearly opaque
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, massive, spherical
- Cleavage
- Distinct on {001} and {100}
- Rarity
- Uncommon
- Uses
- Collector, Scientific research
- Host rock
- A widespread product of low-grade metamorphism of amygdaloidal basalts and diabases; in glaucophane schists and in graywackes
Where rockhounds find pumpellyite-(mg)
Classic worldwide localities
- Calumet, Houghton Co., on the Keweenaw Peninsula and Isle Royale, Michigan, USA
- Skaggs Springs, 24 km northwest of Healdsburg, and at Novato and Porter Creek, Sonoma Co., California, USA
- Lendalfoot, Aryshire, Scotland
- Great Penhaver Point, Roseland, and in the Penlee quarry, Newlyn, Cornwall, England
- Knipane, Iveland, Norway
- Herbornseelbach, Hesse, Germany
Field-hunting tip
Where it forms: A widespread product of low-grade metamorphism of amygdaloidal basalts and diabases; in glaucophane schists and in graywackes. If you start seeing chlorite, epidote, actinolite in float, you are in the right ground. Typical habit: fibrous, massive, spherical. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify pumpellyite-(mg)?+
Where is pumpellyite-(mg) found?+
What rocks look like pumpellyite-(mg)?+
What minerals are found with pumpellyite-(mg)?+
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What is pumpellyite-(mg) used for?+
Find pumpellyite-(mg) on the map
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