Labradorite. Char­ac­ter­is­tics, gen­e­sis, dis­tri­b­u­tion

Labradorite is a major plu­ton­ic rock from the gab­broide fam­i­ly. The name labradorite is derived from the min­er­al labradorite, which makes up this rock. The name of the min­er­al comes from the name of the Labrador Penin­su­la, where it was first dis­cov­ered.

Labradorite is includ­ed in the list of min­er­als of nation­al impor­tance approved by the Res­o­lu­tion of the Cab­i­net of Min­is­ters of Ukraine dat­ed Decem­ber 12, 1994, No. 827, as a raw mate­r­i­al for fac­ing mate­ri­als (dec­o­ra­tive stones).

Properties of labradorites

The rocks of this group con­sist of pla­gio­clase and pyrox­ene, less often olivine and horn­blende, and the sil­i­ca con­tent ranges from 44 to 53%. In terms of alka­li con­tent, they belong to the nor­mal alka­lin­i­ty range.

Labradorite is a type of anorthosite, which con­sists of 90–100% basic pla­gio­clase, most com­mon­ly labradorite, bitovnite, and less com­mon­ly anor­thite.

In terms of min­er­al com­po­si­tion, labradorite con­sists almost exclu­sive­ly of labradorite, with pyrox­ene, augite, titano­mag­netite, ilmenite and apatite as impu­ri­ties.

Most often, labradorites are grey­ish-white, dark grey, green­ish, or almost black. They are mas­sive in tex­ture and have a full-crys­talline, coarse- and giant-grained struc­ture. The most char­ac­ter­is­tic fea­ture of these rocks is iri­des­cence, an opti­cal effect that aris­es due to the pecu­liar­i­ties of the Labrador crys­tal lat­tice struc­ture. Iri­des­cence appears as bright, mul­ti-coloured flash­es of light on the sur­face of the min­er­al, which vary depend­ing on the view­ing angle and light­ing.

Labradorite deposits are con­fined to large mas­sifs (batholiths, rods, lacol­iths) of intru­sive rocks with con­sis­tent com­po­si­tion and qual­i­ty of stones in terms of area and depth.

Qual­i­ty assess­ment is car­ried out in accor­dance with DSTU stan­dards. The most impor­tant prop­er­ties are strength, den­si­ty, bulk den­si­ty, poros­i­ty, water absorp­tion, water resis­tance, frost resis­tance, wear, tough­ness, etc.

Basic phys­i­cal and mechan­i­cal prop­er­ties of labradorite:

• Bulk den­si­ty — 2.6–2.9 t/m³;
• Poros­i­ty — 0.4–2.9%;
• Com­pres­sive strength: in dry state — 47–262 MPa, in water-sat­u­rat­ed state — 47–232 MPa;
• Water absorp­tion — 0–0.4 %;
• Wear resis­tance — 0.5 g/cm²;
• Melt­ing point 1250–1320°C

Labradorites in Ukraine

Labradorite deposits in Ukraine are con­fined to the Korosten plu­ton of the Ukrain­ian Shield.

Three types of labradorite are dis­tin­guished by their dec­o­ra­tive qual­i­ties:

• dark grey and black Golovin­sky type with grain size up to 10–12 cm with blue, green-blue and gold­en iri­des­cence (Golovynske, Fedorivske, Hor­bu­livske, Slo­bidske deposits in Zhy­to­myr region);
• light grey and grey of the Turchin type with grain size up to 3 cm with blue and sil­ver iri­des­cence (deposits of Synyi Kamin, Kami­an­na Pich, Huta Dobrynske in Zhy­to­myrs­ka oblast; Likarivske in Kirovohrad­s­ka oblast);
• grey, light grey of the Kropy­vnyan­sky type, medi­um to coarse-grained, some­times slight­ly por­phyrit­ic, with­out iridi­s­a­tion (Kropy­vnyanske, Vaskovytske, Isakivske deposits in Zhy­to­myr region).

The first two groups of iri­des­cent vari­eties are the most pop­u­lar for dec­o­ra­tive pur­pos­es. Labradorites with dark grey and black colour occur among gab­broids in the form of lentic­u­lar and rod-shaped bod­ies. Most of them are char­ac­terised by high block­i­ness.

Among Ukrain­ian deposits, many have trade names that are recog­nised world­wide. Among them: Extra Blue Ukraine (Dobrynske deposit), Galac­tic Blue (Ocheretyanske deposit), Vol­ga Blue (Kami­anobridske deposit), Vol­ga Blue Extra (Hor­bu­livske deposit), Sil­ver Grey (Kovalivske deposit), Iri­na Blue (Osnykivske deposit), Black Ice (Nevyrivske deposit), Flower of Ukraine (Fedorivske and Hor­bu­livske deposits), and oth­ers.

Labradorites in the world

Labradorites are wide­ly dis­trib­uted in the world, but the most impor­tant deposits are locat­ed in Cana­da, Mada­gas­car, India and Scan­di­navia.

Cana­da is one of the largest sup­pli­ers of labradorite. High-qual­i­ty labradorites with a full range of iri­des­cence are pro­duced in many large deposits on the Labrador Penin­su­la. The deposits near Labrador City and the Ten Mile Bay deposit pro­duce high-qual­i­ty gems. Oth­er well-known finds come from the Pauls Bay area of Baf­fin Island, the Muskox Intru­sion in the North­west Ter­ri­to­ries, and the peg­matite deposits of the Burin Penin­su­la in New­found­land.

Mada­gas­car is also a leader in labradorite min­ing. In the south of the island, in the Man­an­jari region, labradorites with excep­tion­al­ly bright and colour­ful iri­des­cence are mined. Mada­gas­car labradorite is high­ly val­ued in jew­ellery and col­lect­ing.

Labradorite deposits have been found in many regions of India. They are asso­ci­at­ed with peg­matite for­ma­tions in the states of Oris­sa and Andhra Pradesh, as well as with allu­vial deposits in the south­ern regions, where they are mined as gem­stones. Although Indi­an labradorites have less vivid iri­des­cence than Cana­di­an or Mada­gas­car labradorites, they are also used in jew­ellery.

Labradorite deposits in Scan­di­navia are often exploit­ed as fac­ing stones. The Eve-Ive­land region in south­ern Nor­way is rich in peg­matite and anorthosite deposits.

Lim­it­ed extrac­tion of labradorite is also car­ried out on the island of Green­land.

Applications of labradorite

Labradorites are most com­mon­ly used as dec­o­ra­tive and fac­ing stones, for the man­u­fac­ture of cer­tain inte­ri­or ele­ments (coun­ter­tops, tables, win­dow sills, etc.), sculp­tures, fig­urines, and jew­ellery.

There are sig­nif­i­cant deposits of labradorite in Ukraine, par­tic­u­lar­ly in Zhy­to­myr and Kirovohrad regions, mak­ing it an impor­tant mate­r­i­al for the con­struc­tion and dec­o­ra­tive indus­tries. How­ev­er, to pre­serve nat­ur­al resources, the devel­op­ment and use of these deposits require care­ful plan­ning and an envi­ron­men­tal­ly friend­ly approach.