Tranquillityite is a complex silicate mineral first discovered in lunar basalt samples returned from the Apollo 11 mission. It is a rare accessory mineral found in specific iron-rich igneous rocks, appearing as tiny, dark, non-fluorescent grains that often contain measurable amounts of radioactive elements.
Is this tranquillityite?
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 tranquillityite with a known reference. Tranquillityite sits at Mohs 5-6, 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: dark red.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: inclusions, lath, thin.
Often confused with
Tranquillityite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Zircon is the harder of the two (Mohs 7.5 vs. 5-6); streak differs, so Tranquillityite leaves brown, Zircon leaves white; luster reads submetallic on Tranquillityite and vitreous to adamantine; greasy when metamict on Zircon.
How to tell apart: Streak differs, so Tranquillityite leaves brown, Baddeleyite leaves white to brownish white; luster reads submetallic on Tranquillityite and greasy to vitreous; nearly submetallic in black crystals on Baddeleyite.
How to tell apart: Streak differs, so Tranquillityite leaves brown, Ilmenite leaves black to reddish brown; luster reads submetallic on Tranquillityite and metallic to submetallic on Ilmenite.
Often found alongside tranquillityite
Minerals reported to co-occur with tranquillityite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₈Ti₃Zr₂Si₃O₂₄
- Mohs hardness
- 5-6
- Density
- 4.7 g/cm³
- Colors
- Streak
- Brown
- Luster
- Submetallic
- Transparency
- Opaque to semitransparent
- Crystal system
- Hexagonal
- Crystal habit
- Inclusions, lath, thin
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- A late-stage crystallization product of lunar basaltic magma
Where rockhounds find tranquillityite
Classic worldwide localities
- Moon, at the Apollo 11, 12, 14, 16, and 17 collection sites
Field-hunting tip
Where it forms: A late-stage crystallization product of lunar basaltic magma. If you start seeing troilite, pyroxferroite, tridymite in float, you are in the right ground. Typical habit: inclusions, lath, thin. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify tranquillityite?+
Where is tranquillityite found?+
Is tranquillityite safe to handle?+
What rocks look like tranquillityite?+
What minerals are found with tranquillityite?+
What kind of rock does tranquillityite form in?+
What is tranquillityite used for?+
Find tranquillityite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
