Fogoite-(Y) is an extremely rare silicate mineral discovered in the alkaline volcanic rocks of Fogo Island. It typically occurs as small, transparent prismatic crystals within cavities, often associated with other rare-earth bearing minerals.
Is this fogoite-(y)?
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 fogoite-(y) with a known reference. Fogoite-(Y) sits at Mohs ~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: colorless, creamy white.
- 5Look at form & habitCrystal system: triclinic. Typical habit: prismatic crystals.
Often confused with
Fogoite-(Y) vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside fogoite-(y)
Minerals reported to co-occur with fogoite-(y). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₃Ca₂Y₂Ti(Si₂O₇)₂OF₃
- Mohs hardness
- ~5
- Density
- 3.523 g/cm³
- Colors
- ColorlessCreamy white
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Triclinic
- Crystal habit
- Prismatic crystals
- Cleavage
- Very good on {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In miarolitic cavities in a syenite xenolith in trachytic ejecta from a stratavolcano
Where rockhounds find fogoite-(y)
Classic worldwide localities
- Fogo Island, Cape Verde
Field-hunting tip
Where it forms: In miarolitic cavities in a syenite xenolith in trachytic ejecta from a stratavolcano. If you start seeing sanidine, astrophyllite, fluornatropyrochlore in float, you are in the right ground. Typical habit: prismatic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify fogoite-(y)?+
Where is fogoite-(y) found?+
What rocks look like fogoite-(y)?+
What minerals are found with fogoite-(y)?+
What kind of rock does fogoite-(y) form in?+
What is fogoite-(y) used for?+
Find fogoite-(y) on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
