Borolanite is one of the most remarkable rocks

Rock (geology)

In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

 of the British Isles

British Isles

The British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...

, found on the shores of Loch Borolan (Loch Borralan) in Sutherland

Sutherland

Sutherland is a registration county, lieutenancy area and historic administrative county of Scotland. It is now within the Highland local government area. In Gaelic the area is referred to according to its traditional areas: Dùthaich 'IcAoidh , Asainte , and Cataibh...

, after which it has been named. In this locality there is a considerable area 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...

 rich in red alkali

Alkali

In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...

 feldspar

Feldspar

Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....

, and passing, by diminution in the amount of its 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,...

, into quartz-syenite

Syenite

Syenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or present in relatively small amounts Syenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or...

s and syenites. At the margins of the outcrop patches of nepheline syenite

Nepheline syenite

Nephelene syenite is a holocrystalline plutonic rock that consists largely of nepheline and alkali feldspar. The rocks are mostly pale colored, grey or pink, and in general appearance they are not unlike granites, but dark green varieties are also known...

 occur; usually the nepheline is decomposed, but occasionally it is well preserved; the other ingredients of the rock are brown garnet

Garnet

The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" may come from either the Middle English word gernet meaning 'dark red', or the Latin granatus , possibly a reference to the Punica granatum , a plant with red seeds...

 (melanite) and aegirine

Aegirine

Aegirine is a member of the clinopyroxene group of inosilicates. Aegirine is the sodium endmember of the aegirine-augite series. Aegirine has the chemical formula NaFeSi2O6 in which the iron is present as Fe3+. In the aegirine-augite series the sodium is variably replaced by calcium with iron and...

. The abundance of melanite is very unusual in igneous rocks, though some syenites, leucitophyres, and aegirine-felsite

Felsite

Felsite is a very fine grained volcanic rock that may or may not contain larger crystals. Felsite is a field term for a light colored rock that typically requires petrographic examination or chemical analysis for more precise definition...

s resemble borolanite in this respect. In places the nepheline syenite assumes the form of a dark rock with large rounded white spots. These last consist of an intermixture of nepheline or sodalite

Sodalite

Sodalite is a rich royal blue mineral widely enjoyed as an ornamental gemstone. Although massive sodalite samples are opaque, crystals are usually transparent to translucent...

 and alkali-feldspar. From the analogy of certain leucite syenites which are known in Arkansas

Arkansas

Arkansas is a state located in the southern region of the United States. Its name is an Algonquian name of the Quapaw Indians. Arkansas shares borders with six states , and its eastern border is largely defined by the Mississippi River...

, it is very probable that these spots represent original leucite

Leucite

Leucite is a rock-forming mineral composed of potassium and aluminium tectosilicate K[AlSi2O6]. Crystals have the form of cubic icositetrahedra but, as first observed by Sir David Brewster in 1821, they are not optically isotropic, and are therefore pseudo-cubic. Goniometric measurements made by...

s which have been changed into aggregates of the above-named mineral

Mineral

A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

s. They resemble leucite in their shape, but have not yet been proved to have its crystal

Crystal

A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...

line outlines. The pseudo-leucites, as they have been called, measure one-quarter to three-quarters of an inch across. The dark matrix consists of biotite

Biotite

Biotite is a common phyllosilicate mineral within the mica group, with the approximate chemical formula . More generally, it refers to the dark mica series, primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more aluminous endmembers...

, aegirine-augite and melanite. Connected with the borolanite there are other types of nepheline syenite and pegmatite

Pegmatite

A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....

. In Finland

Finland

Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...

, melanite bearing nepheline rocks have been found and described as ijolite

Ijolite

Ijolite , is an igneous rock consisting essentially of nepheline and augite. Ijolite is a rare rock type of considerable importance from a mineralogical and petrological standpoint...

, but the only other locality for melanite-leucite-syenite is Magnet Cove igneous complex

Magnet Cove igneous complex

The Magnet Cove igneous complex is a small alkalic ring complex lying to the west of the town of Magnet Cove in Hot Spring County, Arkansas. It and the adjacent town are so named due to the existence of magnetite and the terrain being a cove, a basin-shaped valley.The complex is of Mesozoic age,...

in Arkansas.