Tranquillityite
Encyclopedia
Tranquillityite is silicate mineral with an average formula (Fe2+,Ca)8(Zr,Y)2Ti3
(SiO4)3O4. It is mostly composed of iron
, oxygen
, silicon
, zirconium
and titanium
with smaller fractions of yttrium
and calcium
. It is named after the Mare Tranquillitatis
(Sea of Tranquility), the place on the Moon where it was found during the Apollo 11
and 12
missions in 1969. It was identified in 1971 and later found in lunar rocks from all Apollo missions. Together with armalcolite
and pyroxferroite
, it is one of the three minerals which were discovered on the Moon. Fragments of tranquillityite were later found in Northwest Africa, in the NWA 856 Martian meteorite. Tranquillityite of terrestrial origin has been found in Western Australia
.
, pyroxferroite, cristobalite
and alkali feldspar
. The mineral is nearly opaque and appears dark red-brown in thin crystals. It usually contains minor impurities of Al, Mn, Cr, Nb and rare-earth elements (parts per million), as well as up to 0.01% of uranium
. Presence of significant amount of uranium allowed to estimate the age of tranquillityite and some associated minerals in Apollo 11 samples as 3710 million years using the uranium-lead dating
technique. Irradiation by alpha particle
s generated by the uranium decay is believed to be the origin of the predominantly amorphous structure of tranquillityite. Its crystals were obtained by annealing the samples at 800 °C for 30 minutes. Longer annealing did not improve the crystalline quality, and annealing at higher temperatures resulted in spontaneous fracture of samples.
The crystals were initially found to have a hexagonal
crystal structure with the lattice parameters, a = 1.169 nm, c = 2.225 nm and three formula units per unit cell, but later reassigned a face-centered cubic
structure (fluorite
-like). A tranquillityite-like crystalline phase has been synthesized by mixing oxide powders in an appropriate ratio, determined from the chemical analysis of the lunar samples, and annealing the mixture at 1500 °C. This phase was not pure, but intergrown with various intermetallic compounds.
(SiO4)3O4. It is mostly composed of iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
, oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
, zirconium
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
and titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
with smaller fractions of yttrium
Yttrium
Yttrium is a chemical element with symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and it has often been classified as a "rare earth element". Yttrium is almost always found combined with the lanthanides in rare earth minerals and is...
and calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
. It is named after the Mare Tranquillitatis
Mare Tranquillitatis
Mare Tranquillitatis is a lunar mare that sits within the Tranquillitatis basin on the Moon. The mare material within the basin consists of basalt formed in the intermediate to young age group of the Upper Imbrian epoch. The surrounding mountains are thought to be of the Lower Imbrian epoch, but...
(Sea of Tranquility), the place on the Moon where it was found during the Apollo 11
Apollo 11
In early 1969, Bill Anders accepted a job with the National Space Council effective in August 1969 and announced his retirement as an astronaut. At that point Ken Mattingly was moved from the support crew into parallel training with Anders as backup Command Module Pilot in case Apollo 11 was...
and 12
Apollo 12
Apollo 12 was the sixth manned flight in the American Apollo program and the second to land on the Moon . It was launched on November 14, 1969 from the Kennedy Space Center, Florida, four months after Apollo 11. Mission commander Charles "Pete" Conrad and Lunar Module Pilot Alan L...
missions in 1969. It was identified in 1971 and later found in lunar rocks from all Apollo missions. Together with armalcolite
Armalcolite
Armalcolite is a titanium-rich mineral with the chemical formula Ti2O5. It was first found at Tranquility Base on the Moon in 1969 and named for Armstrong, Aldrin and Collins, the three Apollo 11 astronauts. Together with tranquillityite and pyroxferroite, it is one of the three minerals which...
and pyroxferroite
Pyroxferroite
Pyroxferroite SiO3 is a silicate mineral of the pyroxene group. It is mostly composed of iron, silicon and oxygen, with smaller fractions of calcium and several other metals. Together with armalcolite and tranquillityite, it is one of the three minerals which were discovered on the Moon. It was...
, it is one of the three minerals which were discovered on the Moon. Fragments of tranquillityite were later found in Northwest Africa, in the NWA 856 Martian meteorite. Tranquillityite of terrestrial origin has been found in Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
.
Properties
Tranquillityite forms thin stripes up to 15 by 65 micrometres in size in basaltic rocks, where it was produced at a late crystallization stage. It is associated with troiliteTroilite
Troilite is a rare iron sulfide mineral with the simple formula of FeS. It is the iron rich endmember of the pyrrhotite group. Pyrrhotite has the formula FeS which is iron deficient...
, pyroxferroite, cristobalite
Cristobalite
The mineral cristobalite is a high-temperature polymorph of silica, meaning that it has the same chemical formula, SiO2, but a distinct crystal structure. Both quartz and cristobalite are polymorphs with all the members of the quartz group which also include coesite, tridymite and stishovite...
and alkali feldspar
Feldspar
Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
. The mineral is nearly opaque and appears dark red-brown in thin crystals. It usually contains minor impurities of Al, Mn, Cr, Nb and rare-earth elements (parts per million), as well as up to 0.01% of uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
. Presence of significant amount of uranium allowed to estimate the age of tranquillityite and some associated minerals in Apollo 11 samples as 3710 million years using the uranium-lead dating
Uranium-lead dating
Uranium-lead is one of the oldest and most refined of the radiometric dating schemes, with a routine age range of about 1 million years to over 4.5 billion years, and with routine precisions in the 0.1-1 percent range...
technique. Irradiation by alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
s generated by the uranium decay is believed to be the origin of the predominantly amorphous structure of tranquillityite. Its crystals were obtained by annealing the samples at 800 °C for 30 minutes. Longer annealing did not improve the crystalline quality, and annealing at higher temperatures resulted in spontaneous fracture of samples.
The crystals were initially found to have a hexagonal
Hexagonal crystal system
In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...
crystal structure with the lattice parameters, a = 1.169 nm, c = 2.225 nm and three formula units per unit cell, but later reassigned a face-centered cubic
Cubic crystal system
In crystallography, the cubic crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals....
structure (fluorite
Fluorite
Fluorite is a halide mineral composed of calcium fluoride, CaF2. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon...
-like). A tranquillityite-like crystalline phase has been synthesized by mixing oxide powders in an appropriate ratio, determined from the chemical analysis of the lunar samples, and annealing the mixture at 1500 °C. This phase was not pure, but intergrown with various intermetallic compounds.