Gab­bro is an intru­sive igneous, uni­form­ly grained rock com­posed of basic pla­gio­clase, mon­o­clin­ic pyrox­ene, olivine, or horn­blende. The col­or palette of the stone is quite diverse, includ­ing var­i­ous shades of gray and black, some­times with inclu­sions of mala­chite, jade, or even vio­let tones. Most com­mon­ly, gab­bro appears dark gray or black.

This rock is char­ac­ter­ized by high strength, low water absorp­tion, high den­si­ty, and hard­ness. It pol­ish­es well and is resis­tant to weath­er­ing, frost, and mechan­i­cal wear. The tex­ture is mas­sive, some­times with a mot­tled pat­tern due to min­er­al inclu­sions. These prop­er­ties make it a valu­able dec­o­ra­tive and con­struc­tion mate­r­i­al.

Gab­bro 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 fac­ing mate­ri­als (dec­o­ra­tive stone) and as a source for rub­ble stone and crushed stone.

Types of Gabbro

Based on min­er­al com­po­si­tion, gab­bro is divid­ed into sev­er­al types: anorthosites, norites, and troc­to­lites. Anorthosites con­tain almost no dark-col­ored min­er­als and are rich in pla­gio­clase (85–90 %). Labradorites are dis­tin­guished among anorthosites — rocks com­posed main­ly of labrador. They are char­ac­ter­ized by a beau­ti­ful bluish, pur­ple or green­ish play of col­ors, which is relat­ed to the opti­cal prop­er­ties of the labrador and is called iri­des­cence.

Norites are dis­tin­guished by the pres­ence of both mon­o­clin­ic and orthopy­rox­ene in sig­nif­i­cant amounts, where­as troc­to­lites con­sist exclu­sive­ly of pla­gio­clase and olivine. Gab­bro con­tain­ing more than 5% olivine is called olivine gab­bro.

There are also anal­cime gab­bros, which are iden­ti­cal to tesh­en­ite rocks. The gab­bro fam­i­ly also includes gabroids (gab­broic rocks) — coarse-grained igneous rocks, sim­i­lar in com­po­si­tion and tex­ture to gab­bro.

Gabbro extraction

Since gab­bro belongs to pro­cess­ing stones, the extrac­tion of blocks from it rep­re­sents the great­est val­ue for the devel­op­er. Gab­bro is main­ly mined by open-pit meth­ods in quar­ries, using drilling and blast­ing oper­a­tions, rock-break­ing machines, and mod­ern stone-cut­ting tech­nolo­gies. The most waste-free tech­nol­o­gy for extract­ing blocks is wire saw­ing using dia­mond wire.

If there is no such equip­ment, then all that remains is to extract irreg­u­lar­ly shaped blocks by break­ing the stone (explo­sion and oth­er meth­ods) and cut them to the cor­rect shape.

Processing

Grind­ing is the rough­est stage, which allows you to get rid of irreg­u­lar­i­ties of half a mil­lime­ter or less. The sur­face will remain rough. An abra­sive or dia­mond tool is used for grind­ing.

Pol­ish­ing of gab­bro and oth­er nat­ur­al stone is the stage at which the sur­face becomes reflec­tive, like a mir­ror. Pol­ish­ing discs and var­i­ous chem­i­cal com­pounds are used for this pur­pose. Before pro­cess­ing, the stone has an incon­spic­u­ous light gray shade. How­ev­er, after pol­ish­ing, its sur­face acquires a rich black col­or.

Sand­blast­ing is used for stone engrav­ing.

Distribution of gabbro

Gab­bro forms lac­col­iths, lopo­lites, intru­sive deposits, dikes and rods. Its mas­sifs are found in both con­ti­nen­tal and ocean­ic regions, hav­ing dif­fer­ent ages — from Archean to mod­ern.

Most gab­bro is con­cen­trat­ed in plu­ton­ic bod­ies, although it some­times occurs as a coarse-grained facies of cer­tain lavas. Gab­bro can be formed in the form of a mas­sive homo­ge­neous intru­sion due to the crys­tal­liza­tion of pyrox­ene and pla­gio­clase in place or in the form of cumu­lates that occur dur­ing the depo­si­tion of these min­er­als in lay­ered intru­sions.

Although gab­bro and gabroids are some­times part of batholiths, their pro­por­tion there is insignif­i­cant due to the high den­si­ty of iron- and cal­ci­um-con­tain­ing mag­mas. At the same time, gab­bro is a key com­po­nent of the ocean­ic crust and is com­mon in ophi­o­lite com­plex­es as a lay­ered gab­bro. Sim­i­lar for­ma­tions are formed in mag­ma cham­bers under mid-ocean ridges.

Lay­ered gab­bro is also char­ac­ter­is­tic of lopoliths—large, saucer-shaped intru­sions, most­ly of Pre­cam­bri­an age. Notable exam­ples include the Bushveld Com­plex (South Africa), the Muskux intru­sion (Cana­da), the Rum Island com­plex (Scot­land), the Still­wa­ter Com­plex (USA), and mas­sifs near Sta­vanger (Nor­way). Gab­bro is also com­mon in alka­line vol­can­ism asso­ci­at­ed with con­ti­nen­tal rift­ing.

In Ukraine, gab­bro is asso­ci­at­ed with the Ukrain­ian Shield. The most well-known occur­rences are found in the Korosten Plu­ton (Zhy­to­myr region), the Korsun–Novomyrhorod Plu­ton (Kirovohrad block), and the Azov block (basins of the Kalmius and Kalchyk rivers). The largest deposits are locat­ed in the Zhy­to­myr region (Holovynske, Turchynske, Rud­nia Shli­akho­va, and oth­ers).

Uses

Prod­ucts made from gab­bro are dis­tin­guished by their unique col­or and inter­est­ing tex­ture, as well as high strength, hard­ness, heat resis­tance, and wear resis­tance.

Norites dif­fer in the pres­ence of both mon­o­clin­ic and rhom­bic pyrox­ene in notable amounts, while troc­to­lites con­sist exclu­sive­ly of pla­gio­clase and olivine. A gab­bro with more than 5% olivine is called an olivine gab­bro. Most com­mon­ly, the stone is used in con­struc­tion (as blocks) and for cladding (fac­ing slabs are usu­al­ly pol­ished). Recent­ly, gab­bro has also been used as a mate­r­i­al for curb­stones, as well as in the pro­duc­tion of win­dow sills and coun­ter­tops, and it has gained atten­tion from mon­u­ment man­u­fac­tur­ers. Addi­tion­al­ly, this stone is used in the pro­duc­tion of road stone and crushed stone. The main advan­tages of this black (and some­times dark green) stone are its resis­tance to low tem­per­a­tures and its strength.