Ferriandrosite-(La) is a rare member of the allanite group, typically occurring as dark, submetallic prismatic crystals. It is primarily found in hydrothermal veins associated with metamorphic or volcanic processes, making it a prized species for advanced systematic mineral collectors.
Is this ferriandrosite-(la)?
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 ferriandrosite-(la) with a known reference. Ferriandrosite-(La) sits at Mohs 6-6.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Ferriandrosite-(La) leaves a brownish gray streak.
- 3Read the lusterHold the specimen under a strong light. Ferriandrosite-(La) typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: black, dark brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic, elongated crystals.
Often confused with
Ferriandrosite-(La) vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Ferriandrosite-(La) leaves brownish gray, Allanite leaves gray; luster reads vitreous on Ferriandrosite-(La) and submetallic on Allanite.
How to tell apart: Streak differs, so Ferriandrosite-(La) leaves brownish gray, Epidote leaves white.
Often found alongside ferriandrosite-(la)
Minerals reported to co-occur with ferriandrosite-(la). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mn²⁺La³⁺Fe³⁺AlMn²⁺(Si₂O₇)(SiO₄)O(OH)
- Mohs hardness
- 6-6.5
- Density
- 4.2-4.4 g/cm³
- Colors
- Streak
- Brownish Gray
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic, Elongated Crystals
- Cleavage
- Imperfect On {001}
- Rarity
- Rare
- Uses
- Collector, Scientific Research
- Host rock
- Hydrothermal Veins in Volcanic Rocks
Where rockhounds find ferriandrosite-(la)
Classic worldwide localities
- Capo di Monte, Viterbo, Italy
- Tuscany, Italy
Field-hunting tip
Look in hydrothermal veins in volcanic rocks country, the host setting where ferriandrosite-(la) typically forms. If you start seeing quartz, albite, epidote in float, you are in the right ground. Field specimens usually show a prismatic, elongated crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferriandrosite-(la)?+
Where is ferriandrosite-(la) found?+
What rocks look like ferriandrosite-(la)?+
What minerals are found with ferriandrosite-(la)?+
What kind of rock does ferriandrosite-(la) form in?+
What is ferriandrosite-(la) used for?+
Find ferriandrosite-(la) on the map
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