Luxullianite is a rare type of granite

Granite

Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...

, notable for the presence of clusters of radially arranged acicular tourmaline

Tourmaline

Tourmaline is a crystal boron silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-precious stone and the gem comes in a wide variety of colors...

 crystals enclosed by phenocryst

Phenocryst

thumb|right|300px|[[Granite]]s often have large [[feldspar|feldspatic]] phenocrysts. This granite, from the [[Switzerland|Swiss]] side of the [[Mont Blanc]] massif, has large white [[plagioclase]] phenocrysts, [[triclinic]] [[mineral]]s that give [[trapezium|trapezoid]] shapes when cut through)...

s of orthoclase

Orthoclase

Orthoclase is an important tectosilicate mineral which forms igneous rock. The name is from the Greek for "straight fracture," because its two cleavage planes are at right angles to each other. Alternate names are alkali feldspar and potassium feldspar...

 and quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

 in a matrix

Matrix (geology)

The matrix or groundmass of rock is the finer grained mass of material in which larger grains, crystals or clasts are embedded.The matrix of an igneous rock consists of finer grained, often microscopic, crystals in which larger crystals are embedded. This porphyritic texture is indicative of...

 of quartz, tourmaline, alkali feldspar, brown mica

Mica

The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition...

, and cassiterite

Cassiterite

Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem...

.

The name originates from the village of Luxulyan

Luxulyan

Luxulyan , also spelled Luxullian or Luxulian, is a village and civil parish in central Cornwall, United Kingdom. The village lies four miles northeast of St Austell and six miles south of Bodmin...

 in Cornwall

Cornwall

Cornwall is a unitary authority and ceremonial county of England, within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall has a population of , and covers an area of...

, England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

, where this type of granite is found. An example may be seen in the Duke of Wellington

Arthur Wellesley, 1st Duke of Wellington

Field Marshal Arthur Wellesley, 1st Duke of Wellington, KG, GCB, GCH, PC, FRS , was an Irish-born British soldier and statesman, and one of the leading military and political figures of the 19th century...

's monument at St Paul's Cathedral

St Paul's Cathedral

St Paul's Cathedral, London, is a Church of England cathedral and seat of the Bishop of London. Its dedication to Paul the Apostle dates back to the original church on this site, founded in AD 604. St Paul's sits at the top of Ludgate Hill, the highest point in the City of London, and is the mother...

 in London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

.

External links

• http://www.ucl.ac.uk/~ucfbrxs/PLM/tourmaline.html Microscopic images of Luxullianite showing the crystal formations.