Magnesiochloritoid is a rare member of the chloritoid group found in high-pressure, low-temperature metamorphic environments. It typically appears as dark, tabular or platy crystals embedded within schistose host rocks, often requiring microscopic examination for positive identification.
Is this magnesiochloritoid?
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 magnesiochloritoid with a known reference. Magnesiochloritoid sits at Mohs 6.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: gray white.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly.
- 4Match the color rangeCompare against the expected color range: greenish gray, greenish black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, foliated masses, rosettes.
Often confused with
Magnesiochloritoid vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Magnesiochloritoid leaves gray white, Chloritoid leaves white, grayish, or very slightly greenish; luster reads pearly on Magnesiochloritoid and somewhat pearly on cleavage surfaces on Chloritoid.
How to tell apart: Magnesiochloritoid is noticeably harder (Mohs 6.5 vs. 2-3); streak differs, so Magnesiochloritoid leaves gray white, Mica leaves white.
How to tell apart: Streak differs, so Magnesiochloritoid leaves gray white, Staurolite leaves white to grayish; luster reads pearly on Magnesiochloritoid and subvitreous to resinous on Staurolite.
Often found alongside magnesiochloritoid
Minerals reported to co-occur with magnesiochloritoid. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MgAl₂SiO₅(OH)₂
- Mohs hardness
- 6.5
- Density
- 3.25 g/cm³
- Streak
- Gray white
- Luster
- Pearly
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals, foliated masses, rosettes
- Cleavage
- {001}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In metapelites and related rocks within high-grade blueschist rocks; stable under metamorphic conditions of near 500 °C and 18 kbar
Where rockhounds find magnesiochloritoid
Classic worldwide localities
- Monte Rosa massif, near the Ghiacciaio di Verra, Italy
- Val d'Ayas, near the border with Switzerland, Italy
- Praborna mine, near St. Marcel, Val d'Aosta, Italy
- Zermatt, Valais, Switzerland
- Hohe Tauern Mountains, Austria
Field-hunting tip
Where it forms: In metapelites and related rocks within high-grade blueschist rocks; stable under metamorphic conditions of near 500 °C and 18 kbar. If you start seeing talc, chlorite, muscovite in float, you are in the right ground. Typical habit: tabular crystals, foliated masses, rosettes. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify magnesiochloritoid?+
Where is magnesiochloritoid found?+
What rocks look like magnesiochloritoid?+
What minerals are found with magnesiochloritoid?+
What kind of rock does magnesiochloritoid form in?+
What is magnesiochloritoid used for?+
Find magnesiochloritoid on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
