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. Tranquillityite leaves a brown streak.
- 3Read the lusterHold the specimen under a strong light. Tranquillityite typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: dark brown, reddish brown, opaque black.
- 5Look at form & habitCrystal system: trigonal. Typical habit: anhedral to subhedral grains.
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 adamantine on Zircon.
How to tell apart: Streak differs, so Tranquillityite leaves brown, Baddeleyite leaves white.
How to tell apart: Streak differs, so Tranquillityite leaves brown, Manaccanite leaves black.
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
- (Fe²⁺, Ca, Mg, Y)₈(Zr, Nb)₂(Ti, Fe³⁺)₃Si₃O₂₄
- Mohs hardness
- 5-6
- Density
- 4.8-5.0 g/cm³
- Streak
- Brown
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Anhedral to Subhedral Grains
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Scientific Research
- Host rock
- Lunar Basalt, Terrestrial Mafic Igneous Rocks
- Typical price
- n/a (extremely limited market availability)
Where rockhounds find tranquillityite
Classic worldwide localities
- Moon (Sea of Tranquility)
- Pilbara Craton, Western Australia
Field-hunting tip
Look in lunar basalt, terrestrial mafic igneous rocks country, the host setting where tranquillityite typically forms. If you start seeing fayalite, pyroxene, plagioclase in float, you are in the right ground. Field specimens usually show a anhedral to subhedral grains habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify tranquillityite?+
Where is tranquillityite found?+
How much is tranquillityite worth?+
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.
