Connemara Marble Slabs (geograph 4005264)

Connemara marble or "Irish green" is a rare variety of

marble Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Marble is typically not foliated (layered), although there are exceptions. In geology, the term ''marble'' refers to metamorphose ...

found in

Connemara Connemara (; )( ga, Conamara ) is a region on the Atlantic coast of western County Galway, in the west of Ireland. The area has a strong association with traditional Irish culture and contains much of the Connacht Irish-speaking Gaeltacht, ...

Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...

with a distinct green colour. It is commonly used as a gemstone and for decorations. Due to its colouration, it is commonly associated with the Irish identity. It strongly resembles the

verd antique Verd antique (obsolete French, from Italian, ''verde antico'', "ancient green"), also called verde antique, ''marmor thessalicum'', or Ophite, is a serpentinite breccia popular since ancient times as a decorative facing stone. It is a dark, dull ...

found in the

Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western Europe, Western and Southern Europe and Anatolia, on the south by North Africa ...

. It is named after the region in the western part of the country in which it is quarried (including Lissoughter in Recess, County Galway, and in

Clifden Clifden (, meaning "stepping stones") is a coastal town in County Galway, Ireland, in the region of Connemara, located on the Owenglin River where it flows into Clifden Bay. As the largest town in the region, it is often referred to as "the Capi ...

Geology

Connemara marble occurs as layers within the Connemara Marble Formation from the lower

Dalradian The Dalradian Supergroup (informally and traditionally the Dalradian) is a stratigraphic unit (a sequence of rock strata) in the lithostratigraphy of the Grampian Highlands of Scotland and in the north and west of Ireland. The diverse assembla ...

Appin Group, part of the Connemara Metamorphic Complex. The parent rock was an impure siliceous dolomitic limestone deposited in a shelf environment on the continental margin of

Laurentia Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, althoug ...

. In the Grampian Orogeny it underwent silimanite grade metamorphism. Minerals formed at this stage were a variety of calc-silicates, including

diopside Diopside is a monoclinic pyroxene mineral with composition . It forms complete solid solution series with hedenbergite () and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull ...

forsterite Forsterite (Mg2SiO4; commonly abbreviated as Fo; also known as white olivine) is the magnesium-rich end-member of the olivine solid solution series. It is isomorphous with the iron-rich end-member, fayalite. Forsterite crystallizes in the orthorh ...

tremolite Tremolite is a member of the amphibole group of silicate minerals with composition: Ca2(Mg5.0-4.5Fe2+0.0-0.5)Si8O22(OH)2. Tremolite forms by metamorphism of sediments rich in dolomite and quartz. Tremolite forms a series with actinolite and fe ...

, together with

talc Talc, or talcum, is a clay mineral, composed of hydrated magnesium silicate with the chemical formula Mg3Si4O10(OH)2. Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent a ...

and chlorite. Subsequent

metasomatism Metasomatism (from the Greek μετά ''metá'' "change" and σῶμα ''sôma'' "body") is the chemical alteration of a rock by hydrothermal and other fluids. It is the replacement of one rock by another of different mineralogical and chemical co ...

, probably associated with hydrothermal fluids from the late Caledonian

Galway Galway ( ; ga, Gaillimh, ) is a city in the West of Ireland, in the province of Connacht, which is the county town of County Galway. It lies on the River Corrib between Lough Corrib and Galway Bay, and is the sixth most populous city on ...

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies under ...

s, altered the calc-silicates to minerals of the

serpentine subgroup Serpentine subgroup (part of the kaolinite-serpentine group in the category of phyllosilicates) are greenish, brownish, or spotted minerals commonly found in serpentinite. They are used as a source of magnesium and asbestos, and as decorative ...

. The layers of marble are interbedded with

schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes ...

s and

quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tec ...

s. As a marble, the most important mineral components are

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

and calcite, supplemented with variable amounts of diopside, serpentine, tremolite, forsterite,

clinochlore The chlorites are the group of phyllosilicate minerals common in low-grade metamorphic rocks and in Mineral alteration, altered igneous rocks. Greenschist, formed by metamorphism of basalt or other low-silica volcanic rock, typically contains si ...

phlogopite Phlogopite is a yellow, greenish, or reddish-brown member of the mica family of phyllosilicates. It is also known as magnesium mica. Phlogopite is the magnesium endmember of the biotite solid solution series, with the chemical formula KMg3AlSi3O ...

omphacite Omphacite is a member of the clinopyroxene group of silicate minerals with formula: ( Ca, Na)( Mg, Fe2+, Al) Si2 O6. It is a variably deep to pale green or nearly colorless variety of clinopyroxene. It normally appears in eclogite, which is the ...

and talc. The colour is determined by the coloured mineral content, with serpentine responsible for the characteristic green colouration. Connemara marble differs from the verd antiques in that it is an actual marble, rather than a

serpentinite Serpentinite is a rock composed predominantly of one or more serpentine group minerals, the name originating from the similarity of the texture of the rock to that of the skin of a snake. Serpentinite has been called ''serpentine'' or ''se ...

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...

, despite also having a very high serpentine content.

Uses

Connemara marble is used in souvenirs, jewellery and home decoration. It is not suitable for usage in outside construction as it rapidly loses its colouration due to weathering. It has been quarried since the 1700s, and has been exported throughout Europe and America to make columns, floors and other decorations.

References

{{reflist Connemara Marble National symbols of the Republic of Ireland

Geology

Uses

See also

References