Painite

Painite is a very rare borate mineral. It was first found in Myanmar by British mineralogist and gem dealer Arthur C.D. Pain who misidentified it as ruby, until it was discovered as a new gemstone in the 1950s. When it was confirmed as a new mineral species, the mineral was named after him.

The chemical makeup of painite contains calcium, zirconium, boron, aluminium, and oxygen (CaZrAl9O15(BO3)). The mineral also contains trace amounts of chromium and vanadium, which are responsible for Painite's typically orange-red to brownish-red color, similar to topaz. The mineral's rarity is due to zirconium and boron rarely interacting with each other in nature. The crystals are naturally hexagonal, but may also be euhedral or orthorhombic. They also may have no crystalline structure, but usually are accompanied by a crystalline structure. Until late 2004, only two had been cut into faceted gemstones.

Painite

General

Category Borate minerals

Formula CaZrAl9O15(BO3)

IMA symbol Pai

Strunz classification 6.AB.85

Dana classification 7.5.2.1

Crystal system Hexagonal

Crystal class Dipyramidal (6/m)

(same H-M symbol), although earlier reported as hexagonal (6)

Space group P63/m

Unit cell a = 8.72 Å,

c = 8.46 Å; Z = 2

Identification

Color Red, brownish, orange-red

Crystal habit Elongated crystals, pseudo-orthorhombic

Mohs scale hardness 7.5 – 8

Luster Vitreous

Streak Red

Diaphaneity Transparent

Specific gravity 4.01

Optical properties Uniaxial (-)

Refractive index no = 1.8159, ne = 1.7875

Pleochroism Ruby-red parallel to; pale brownish orange or pale red-orange at right angles to 

Melting point 2094[ambiguous]

Solubility Insoluble in acids

Etymology

Painite was first discovered at Ongaing, near the town of Mogok in the Mandalay Region of Myanmar (formerly Burma), and described in 1957 by Claringbull, Hey and Payne, who named the mineral after Arthur Charles Davy Pain (1901–1971), a British mineralogist and gemologist.

Classification

In the now outdated, but still in use 8th edition of the mineral systematics according to Strunz, painite belonged to the common mineral class of “carbonates, nitrates and borates ” and there to the department of “island borates”, where it formed an independent group together with fluoborite, jeremejewite and karlite.

The 9th edition of Strunz's mineral classification, valid since 2001 and used by the International Mineralogical Association (IMA), classifies painite in the new class of "borates" and within it in the division of "monoborates." However, this division is further subdivided according to the structure of the borate complex and the possible presence of additional anions, so that the mineral, according to its composition, can be found in the subdivision "BO 3 with additional anions; 1(Δ) + OH, etc.", where it is the sole member of the unnamed group 6.AB.85.

In contrast to Strunz's classification, the Dana classification of minerals, which is predominantly used in English-speaking countries, classifies painite in the class of " oxides and hydroxides " and within the division of "multiple oxides." Here, it is found as the only member of the unnamed group 07.05.02 within the subdivision of " multiple oxides with the formula ABX 2. "

Crystal structure

Painite crystallizes hexagonally in the space group P 6 3 (space group no. 173) with lattice parameters a = 8.72 Å and c = 8.47 Å and 2 formula units per unit cell. 

Characteristics

The colors of painite crystals range from brown (sometimes with a strong green tinge) to reddish-brown to red (in all shades from clear to almost black). Some specimens are also light violet to pink. Some pieces, particularly the radiating aggregates, show distinct zoning. Painite is strongly dichroic. Nothing definitive has been published to date about twins of painite, although a few pieces with regular intergrowths have been observed, including one specimen with crystals intergrown at right angles. However, it remains to be seen whether these are actually twins.

Some of the painite (the proportion is currently unknown) exhibits a color change from brown in daylight to reddish-brown in incandescent light. This color change, while clearly visible, has so far been deemed too subtle to be recognized by the only body investigating it.

Discovery and occurrence

Extensive exploration in the area surrounding Mogok, which comprises a large part of the extremely small region the mineral is known to exist in, has identified several new painite occurrences that have been vigorously explored resulting in several thousand new available painite specimens.

Use as a gemstone

Due to its extreme rarity and good physical properties, painite is sometimes processed into valuable gemstones or, due to high demand among mineral collectors, is mined specifically for collection purposes and exported in rough form. No other uses are known.

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