Serendibite

Serendibite is an extremely rare silicate mineral that was first discovered in 1902 in Sri Lanka by Dunil Palitha Gunasekera and named after Serendib, the old Arabic name for Sri Lanka.

The mineral is found in skarns associated with boron metasomatism of carbonate rocks where intruded by granite. Minerals occurring with serendibite include diopside, spinel, phlogopite, scapolite, calcite, tremolite, apatite, grandidierite, sinhalite, hyalophane, uvite, pargasite, clinozoisite, forsterite, warwickite and graphite.

Serendibite

General

Category Inosilicates

Formula (Ca,Na)2(Mg,Fe2+)3(Al,Fe3+)3[O2|(Si,Al,B)6O18]

IMA symbol Ser

Strunz classification 9.DH.40

Dana classification 69.2.1a.6

Crystal system Triclinic

Crystal class Pinacoidal (1)

(same H-M symbol)

Space group P1

Identification

Color pale yellow, blue-green, greyish blue, black

Twinning Polysynthetic on {0–11} is common

Cleavage None observed

Fracture Uncommon, conchoidal

Mohs scale hardness 6.5 – 7

Luster Vitreous

Streak White

Diaphaneity Transparent, Translucent,Opaque

Specific gravity 3.42 – 3.52 (measured) 3.47 (calculated)

Optical properties Biaxial (+)

Refractive index 1.701 – 1.706

Pleochroism Visible,strong, color: green, blue, yellow, light blue, bluegreen, light yellow

2V angle Measured: 80°

Dispersion strong

Etymology

Serendibite was first discovered in 1902 near the town of Gangapitiya in the Central Province of the island nation of Sri Lanka. The following year, it was first scientifically explored and described by George T. Prior and Ananda K. Coomaraswamy. The mineral received its name from the ancient Arabic name for "Sri Lanka" (Serendib). 

Classification

In the outdated, but still partly used 8th edition of the mineral systematics according to Strunz, the serendibite belonged to the section of the " chain and band silicates (inosilicates)", where it formed the "aenigmatite group" with the system number VIII/F.14 together with aenigmatite, dorrite, høgtuvaite, crinovite, makarochkinite, rhönite, sapphirine, welshite and wilkinsonite.

The 9th edition of Strunz's mineral classification, valid since 2001 and used by the International Mineralogical Association (IMA), also classifies serendibite in the division of "chain and band silicates (inosilicates)". However, this division is further subdivided according to the type of chain formation, so that the mineral, according to its structure, can be found in the subdivision "chain and band silicates with 4-periodic single chains, Si 4 O 12 ", where it forms the unnamed group 9.DH.45 together with aenigmatite, baykovite, dorrite, høgtuvaite, khmaralite, crinovite, makarochkinite, rhönite, sapphirine, welshite and wilkinsonite.

Dana's classification of minerals, which is predominantly used in English-speaking countries, also classifies sapphirine in the class of "silicates and germanates," but within the division of "chain silicates: chains with side branches or loops." Here, it is found together with aenigmatite, dorrite, høgtuvaite, crinovite, makarochkinite, rhönite, welshite, and wilkinsonite in the group "Aenigmatite and related species (aenigmatite subgroup)" with the system number 69.02.01a within the subdivision " Chain silicates: chains with side branches or loops with P>2."

The current CNMN classification for the sapphirine group reclassifies it and groups serendibite together with høgtuvaite, makarochkinite, rhönite and welshite in the rhönite group (Ca at the largest M position) below the sapphirine group in the sapphirine supergroup.

Crystal structure

Serendibite crystallizes triclinically in the space group P 1 (space group no. 2). The lattice parameters determined from three mineral samples are a = 10.010(3) to 10.094(3) Å; b = 10.393(3) to 10.478(3) Å; c = 8.631(2) to 8.694(2) Å; α = 106.36(l) to 106.37(1)°; β = 96.00(l) to 96.10(l)° and γ = 124.38(1) to 124.40(l)° as well as two formula units per unit cell. 

Features

Serendibite is a silicate with the chemical formula Ca₄[Mg₆Al₆]O₄[Si₆B₃Al₃O 36 ]. It is a species approved by the International Mineralogical Association, and first published in 1903. It crystallizes in the triclinic system. Its hardness on the Mohs scale ranges between 6.5 and 7.

According to the Nickel-Strunz classification, serendibite belongs to "09.DH - Inosilicates with 4 periodic single chains, Si₄O₁₂" along with the following minerals: leucophanite, ohmilite, hardaite, suzukiite, batysite, shcherbakovite, taikanite, krauskopfite, balangeroite, gageïte, enigmatite, dorrite, høgtuvaite, krinovite, makarochkinite, rhönite, welshite, wilkinsonite, sapphirine, khmaralite, surinamite, deerite, howieite, taneyamalite, johninnesite and agrellite.

Formation and deposits

It was discovered in Gangapitiya, in the town of Ambakotte (Central Province, Sri Lanka). It has also been described in other places in Sri Lanka, Myanmar, Canada, the United States, Tanzania, Madagascar and Russia.

Use as a gemstone

Most serendibite is black and opaque, although some show golden-brown, green, or blue shimmers when viewed through transmitted light. Serendibite is used almost exclusively as a collector's stone and for jewelry. In 2005, new sources were discovered in Mogok, Myanmar; previously, only three faceted stones were known from Sri Lanka.

While the Serendibit from Sri Lanka shows green-blue and violet-blue colors, the varieties from Myanmar are mostly black and opaque.

Sourced from Wikipedia