Gneiss is a gran­u­lar (grain size exceed­ing 0.2–0.3 mm) meta­mor­phic rock with a char­ac­ter­is­tic par­al­lel tex­ture. Gneiss is one of the most wide­spread rock types in the Earth’s crust. They form most of the gran­ite-meta­mor­phic lay­er of the con­ti­nen­tal crust, which are locat­ed on crys­talline shields (for exam­ple, the Baltic, Ukrain­ian, Cana­di­an, Aldan) and form the foun­da­tions of ancient plat­forms (for exam­ple, the Siber­ian plat­form).

Gneiss is the term used by min­ers in Sax­ony since the 16th cen­tu­ry to refer to meta­mor­phic rocks with a par­al­lel tex­ture that con­tain more than 20% feldspar.

Gneiss is includ­ed in the list of min­er­als of nation­al impor­tance, approved by Res­o­lu­tion of the Cab­i­net of Min­is­ters of Ukraine No. 827 of Decem­ber 12, 1994, as a raw mate­r­i­al for rub­ble stone and crushed stone.

General description

It con­sists pre­dom­i­nant­ly of feldspar, as well as quartz and col­ored min­er­als. Sec­ondary min­er­als of gneiss: gar­net, cordierite, dis­ten, sil­li­man­ite and oth­ers.

It is char­ac­ter­ized by a more or less clear­ly defined par­al­lel fine-striped tex­ture, marked by the alter­na­tion of dark and lighter stripes with­out dis­tinct split­ting. Gra­noblas­tic and por­phy­rob­las­tic struc­tures pre­dom­i­nate.

The phys­i­cal prop­er­ties of gneiss are deter­mined by its min­er­alog­i­cal com­po­si­tion and struc­ture. It has high hard­ness (6–7 on the Mohs scale), strength and resis­tance to weath­er­ing, mak­ing it a durable build­ing mate­r­i­al. The col­or of gneiss­es varies from light gray to dark gray, some­times with shades of pink, brown or green­ish. An impor­tant fea­ture is its lay­er­ing, which makes it eas­i­er to split the rock along the strips, but at the same time makes it dif­fi­cult to use in some indus­tries.

Gneiss formation

Gneiss is formed as a result of high-qual­i­ty region­al meta­mor­phic con­di­tions. The rock itself is formed in the depth of the earth­’s crust from 10 to 20 km, at a pres­sure of 10 kilo­bars or more and at a tem­per­a­ture of approx­i­mate­ly 500–700°K. Any water that is present in min­er­als before meta­mor­phism is often lost when the tem­per­a­ture ris­es, lead­ing to stiff­ness. Meta­mor­phic rocks are usu­al­ly resis­tant to dis­so­lu­tion in water.

There are many vari­eties depend­ing on the min­er­al com­po­si­tion and tex­ture, but all gneiss­es are evi­dence of deep defor­ma­tion of the earth­’s crust.

Exter­nal­ly, gneiss­es are often sim­i­lar to gran­ites or oth­er lay­ered rocks, but dif­fer in a greater degree of recrys­tal­liza­tion and dis­tinct stri­a­tion, which makes them eas­i­ly rec­og­niz­able. This is one of the fea­tures that helps dis­tin­guish gneiss from oth­er mul­ti­lay­er rocks. Min­er­al, usu­al­ly includes quartz, feldspar, mica, chlo­rite and oth­er clay min­er­als. Some also include larg­er crys­tals embed­ded in the rock matrix, most often gar­net, topaz, and beryl min­er­als.

Gneiss­es that form dur­ing meta­mor­phism of sed­i­men­ta­ry rocks are usu­al­ly enriched in alu­mi­na and often con­tain min­er­als such as andalusite, sil­li­man­ite, kyan­ite, and gar­net. Such gneiss­es are called high-alu­mi­na.

Gneiss­es of por­phy­rob­last struc­ture, con­tain­ing large por­phy­rob­lasts or por­phy­ro­clasts of feldspars (usu­al­ly micro­cline).

Based on the nature of the orig­i­nal rocks (degree of meta­mor­phism), gneiss­es are clas­si­fied into parag­neiss­es and orthogneiss­es. The first are formed as a result of deep meta­mor­phism of sed­i­men­ta­ry rocks, and the sec­ond — igneous (main­ly vol­canic).

Accord­ing to the min­er­al com­po­si­tion, pla­giogneiss­es, biotite, mus­covite, bicel­lu­lar, amphi­bole, pyrox­ene gneiss­es are dis­tin­guished. Based on struc­ture and tex­ture, gneiss­es can be tree-like, eye-shaped, band­ed, foli­at­ed, and oth­er types.

Com­bined gneiss­es include gran­i­to-gneiss­es, dior­i­to-gneiss­es, etc. The most typ­i­cal gneiss­es occur in ancient Pre­cam­bri­an com­plex­es. Among them are gray gneiss­es, which belong to the old­est rocks on Earth. Active gneiss for­ma­tion occurred around 2.5–2.0 bil­lion years ago. The old­est known rocks today are the gray gneiss of the Akas­to region, which forms the basis of the Cana­di­an Shield’s Archean cra­ton; their age is approx­i­mate­ly 3.92 bil­lion years.

Distribution of the rock

Gneiss is one of the most wide­spread meta­mor­phic for­ma­tions of the Earth­’s crust, com­pris­ing a sig­nif­i­cant part of the granite–metamorphic lay­er of the con­ti­nen­tal crust and wide­ly devel­oped with­in crys­talline shields and fold belts. Its large mas­sifs form the foun­da­tions of ancient plat­forms, in par­tic­u­lar the Siber­ian one, and are also exposed on the Baltic, Ukrain­ian, Cana­di­an and Aldan shields. Sig­nif­i­cant deposits of gneiss­es are known in Scan­di­navia, Brazil, India, South Africa, Aus­tralia and Cen­tral Europe (Ger­many, Czech Repub­lic, Poland).

They form geo­log­i­cal com­plex­es with an area of thou­sands of square kilo­me­ters, so their resources are con­sid­ered prac­ti­cal­ly inex­haustible for the con­struc­tion indus­try.

In Ukraine, gneiss­es are wide­spread with­in the Ukrain­ian Shield, par­tic­u­lar­ly in Zhy­to­myr, Kyiv, Vin­nyt­sia, and Kirovohrad regions. The Zhy­to­myr deposits have the great­est indus­tri­al sig­nif­i­cance, with reserves esti­mat­ed at tens of mil­lions of cubic meters, ensur­ing a long-term per­spec­tive for extrac­tion. Oth­er known deposits are locat­ed in the Prya­zov region and in Dnipropetro­vsk Oblast.

Use of gneiss

Gneiss, due to its phys­i­cal and mechan­i­cal prop­er­ties, strength, and dec­o­ra­tive qual­i­ties, is wide­ly used in con­struc­tion and archi­tec­ture. It is a valu­able mate­r­i­al for foun­da­tions, dams, bridges, and retain­ing walls, as it is high­ly resis­tant to atmos­pher­ic influ­ences and has a long ser­vice life.

Crushed gneiss in the form of crushed stone is used in road and rail­way con­struc­tion, as well as a filler in con­crete and asphalt con­crete mix­tures. Due to the char­ac­ter­is­tic lay­ered pat­tern, gneiss has a sig­nif­i­cant dec­o­ra­tive val­ue and is used as a fac­ing stone for build­ing facades, stairs, plinths, and inte­ri­or details.

Pol­ished slabs give struc­tures an ele­gant appear­ance, which is why gneiss is often used in pub­lic and admin­is­tra­tive build­ings, so it is often used in pub­lic and admin­is­tra­tive build­ings, sculp­tures, and memo­r­i­al com­plex­es.

Cer­tain vari­eties of gneiss con­tain­ing feldspars are used as raw mate­r­i­al for the pro­duc­tion of ceram­ic prod­ucts and min­er­al wool. In Scan­di­navia and Cana­da, gneiss is wide­ly used in urban archi­tec­ture, while in Ukraine, the Zhy­to­myr deposits sup­plied mate­r­i­al for the dec­o­ra­tion of build­ings in Kyiv, Zhy­to­myr, and Vin­nyt­sia. Thus, gneiss com­bines the prac­ti­cal­i­ty of a build­ing stone with the dec­o­ra­tive appeal of a fin­ish­ing mate­r­i­al, which defines its impor­tant role in var­i­ous spheres of the econ­o­my.