Almeidaite is a rare lead-zinc-manganese titanate belonging to the crichtonite group. It is typically found as small, dark, tabular crystals within carbonatite complexes, most notably from the Jacupiranga mine in Brazil.
Is this almeidaite?
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 almeidaite with a known reference. Almeidaite sits at Mohs 6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brown.
- 3Read the lusterHold the specimen under a strong light. Luster: submetallic.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: trigonal. Typical habit: tabular rhombohedral crystals.
Often confused with
Almeidaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Almeidaite is noticeably harder (Mohs 6 vs. 4.5-5); streak differs, so Almeidaite leaves brown, Crichtonite leaves dark gray; luster reads submetallic on Almeidaite and metallic, dull to bright on Crichtonite.
How to tell apart: Lindsleyite is the harder of the two (Mohs 7.5 vs. 6); streak differs, so Almeidaite leaves brown, Lindsleyite leaves gray; luster reads submetallic on Almeidaite and metallic on Lindsleyite.
How to tell apart: Mathiasite is the harder of the two (Mohs 7.5 vs. 6); streak differs, so Almeidaite leaves brown, Mathiasite leaves gray; luster reads submetallic on Almeidaite and metallic on Mathiasite.
Often found alongside almeidaite
Minerals reported to co-occur with almeidaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- PbZn₂(Mn,Y)(Ti,Fe³⁺)₁₈O₃₆(OH,O)₂
- Mohs hardness
- 6
- Density
- 4.68 g/cm³
- Colors
- Streak
- Brown
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Tabular rhombohedral crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In altered dacite 2 meters from a hydrothermal quartz vein
Where rockhounds find almeidaite
Classic worldwide localities
- Novo Horizonte, Bahia, Brazil
Field-hunting tip
Where it forms: In altered dacite 2 meters from a hydrothermal quartz vein. If you start seeing rutile, anatase, hematite in float, you are in the right ground. Typical habit: tabular rhombohedral crystals. Train your eye for that shape before scanning the outcrop.
Common questions
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Find almeidaite on the map
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