Senaite is a complex titanium-rich oxide member of the crichtonite group, often appearing as lustrous, opaque black rhombohedral crystals. It is most sought after by collectors for its occurrence in alpine-type fissures or specific igneous complexes. Careful examination of its crystal symmetry and associations helps distinguish it from more common iron-titanium oxides like ilmenite.
Is this senaite?
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 senaite with a known reference. Senaite 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: brownish black.
- 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: rhombohedral crystals, tabular.
Often confused with
Senaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Senaite leaves brownish black, Ilmenite leaves black to reddish brown; luster reads submetallic on Senaite and metallic to submetallic on Ilmenite.
How to tell apart: Streak differs, so Senaite leaves brownish black, Hematite leaves cherry-red or reddish brown; luster reads submetallic on Senaite and metallic or submetallic to dull on Hematite.
How to tell apart: Streak differs, so Senaite leaves brownish black, Magnetite leaves black; luster reads submetallic on Senaite and metallic to submetallic, may be dull on Magnetite.
Often found alongside senaite
Minerals reported to co-occur with senaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb(Mn,Y,U)(Fe,Zn)₂(Ti,Fe,Cr,V)₁₈(O,OH)₃₈
- Mohs hardness
- >6
- Density
- 5.204-5.301 g/cm³
- Colors
- Streak
- Brownish black
- Luster
- Submetallic
- Transparency
- Opaque, may be transparent in very thin fragments
- Crystal system
- Trigonal
- Crystal habit
- Rhombohedral crystals, tabular
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- In granite or syenite pegmatites; in a hydrothermal deposit; a detrital mineral
Where rockhounds find senaite
Classic worldwide localities
- St. Peters Dome, near Pikes Peak, El Paso Co., Colorado, USA
- Diamantina district, as at Datas, Brazil
- Curralinho, Brazil
- Santa Quitéria, Brazil
- Imbiruçu, Brazil
- Vargeas, Brazil
Field-hunting tip
Where it forms: In granite or syenite pegmatites; in a hydrothermal deposit; a detrital mineral. If you start seeing ilmenite, rutile, magnetite in float, you are in the right ground. Typical habit: rhombohedral crystals, tabular. Train your eye for that shape before scanning the outcrop.
Common questions
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Find senaite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
