Morganite in gem

Morganite is an orange or pink variety of beryl and is also a gemstone. Morganite, also known as "pink beryl", "rose beryl", "pink emerald", and "cesian (or caesian) beryl", is a rare light pink to rose-colored gem-quality variety of beryl. Orange/yellow varieties of morganite can also be found, and color banding is common. It can be routinely heat treated to remove patches of yellow and is occasionally treated by irradiation to improve its color. The pink color of morganite is attributed to Mn2+ ions.

 Morganite is mined in Brazil, Afghanistan, Mozambique, Namibia, the United States, and Madagascar. Morganite has grown in popularity since 2010. Brides and CNN have listed it as a possible alternative to diamond for engagement rings.

Morganite

General

Category beryl

Formula Be3Al2(Si6O18)

Identification

Color Pink

Mohs scale hardness 7.5 to 8

Etymology

Following the discovery of a new locality for rose beryl in Madagascar in 1910, George Kunz proposed the name morganite at a meeting of the New York Academy of Sciences on 5 December 1910 to honour his friend and customer J.P. Morgan for his financial support for the arts and sciences, and his important gifts of gems to the American Museum of Natural History in New York and to the Museum of Natural History in Paris. Morgan was one of the most important gem collectors in the early 1900s – his collection was partly assembled by Tiffany and Company and their chief gemmologist, Kunz.

Morganite is also known as pink beryl, rose beryl, pink emerald, and "cesian (or caesian) beryl".

Characteristics

The pink color of morganite is attributed to Mn2+ ions. Morganite is pleochroic; when it is viewed down its crystallographic axis the color is more pink.

In comparison to emerald, morganite lacks inclusions and fractures, thus making it more durable than emerald.

History

Pink beryl of fine color and good sizes was first discovered on an island off the coast of Madagascar in 1910. It was also known, with other gemstone minerals, such as tourmaline and kunzite, at Pala, California. In December 1910, the New York Academy of Sciences named the pink variety of beryl "morganite" after financier J. P. Morgan.

On October 7, 1989, one of the largest gem morganite specimens ever uncovered, eventually called "The Rose of Maine", was found at the Bennett Quarry in Buckfield, Maine, US. The crystal, originally somewhat orange in hue, was 23 cm (9 in) long and about 30 cm (12 in) across, and weighed (along with its matrix) just over 50 pounds (23 kg).

Before 2011, morganite was unknown in many jewelry stores. But, recently morganite has been increasing in popularity.

Value and popularity

According to a 2017 survey, morganite is the second most popular non-diamond stone, after sapphire. A single carat of morganite can cost about $300.

Morganite is one of the rarest members of the beryl family, second only to red beryl. Due to the scarcity of morganites, especially those of high quality, they tend to be among the most expensive per carat. Ones that are deep pink in color tend to be the most valuable.

Beryl

Beryl is a mineral composed of beryllium aluminium silicate with the chemical formula Be3Al2(SiO3)6. Well-known varieties of beryl include emerald and aquamarine. Naturally occurring hexagonal crystals of beryl can be up to several meters in size, but terminated crystals are relatively rare. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, pink, and red (the rarest). It is an ore source of beryllium.

Classification

Already in the outdated 8th edition of the mineral classification according to Strunz, beryl belonged to the mineral class of “silicates and germanates” and there to the division of “ ring silicates (cyclosilicates)” (with six-membered rings [Si 6 O 18 ] 12−), where it formed the name giver of the “beryl series” with the system no. VIII/C.06a and the other members bazzite and indialite within the “beryl-cordierite group” (no. VIII/C.06).

In the Lapis mineral catalog by Stefan Weiß, last revised and updated in 2018, which, out of consideration for private collectors and institutional collections, still follows this old form of Karl Hugo Strunz 's system, the mineral was given the system and mineral number VIII/E.12-10. In the "Lapis Systematics," this also corresponds to the "Ring Silicates" section, with minerals whose structure consists of six-membered rings [Si 6 O 18 ] 12− being classified in groups VIII/E.12 to 21. Beryl forms an independent, but unnamed group here, together with bazzite, bunnoite, cordierite, ferroindialite, indialite, pezzottaite, sekaninaite, and stoppaniite. 

The 9th edition of Strunz's mineral classification, valid since 2001 and last updated by the International Mineralogical Association (IMA) in 2009, also classifies beryl in the division of "ring silicates". However, this division is further subdivided according to the structure of the silicate rings, so that the mineral, according to its structure, can be found in the subdivision "[Si 6 O 18 ] 12− six-membered simple rings without island-like, complex anions ", where it also forms the eponymous "beryl group" with the system number 9.CJ.05 and the other members bazzite, indialite, pezzottaite and stoppaniite.

Dana's classification of minerals, which is predominantly used in English-speaking countries, also classifies beryl in the class of "silicates and germanates" and within the division of "ring silicates: six-membered rings." Here, it is also found as the namesake of the "beryl group" with the system number 61.01.01, along with the other members bazzite, indialite, stoppaniite, and pezzottaite, within the subdivision " ring silicates: six-membered rings with Si 6 O 18 rings; possible (OH) and Al substitution."

Chemistry

In 100% pure form, which can only be produced synthetically, beryl consists of around 19% aluminum oxide (Al2O3), 14% beryllium oxide (BeO) and 67% silicon dioxide (SiO 2).

Natural beryl can contain various impurities, including rubidium oxide (Rb2O) and cesium oxide (Cs2O). Water of crystallization (H 2 O, up to 3%), as well as argon and helium, can also be embedded in the channels of the ring silicate structure. 

Other possible impurities include lithium and sodium as well as various oxides and hydroxides, halides and/or fluorides. 

Crystal habit and structure

Beryl belongs to the hexagonal crystal system. Normally beryl forms hexagonal columns but can also occur in massive habits. As a cyclosilicate beryl incorporates rings of silicate tetrahedra of SiO3–O (the connected O is from another SiO3) that are arranged in columns along the C axis and as parallel layers perpendicular to the C axis, forming channels along the C axis. These channels permit a variety of ions, neutral atoms, and molecules to be incorporated into the crystal thus disrupting the overall charge of the crystal permitting further substitutions in aluminium, silicon, and beryllium sites in the crystal structure. These impurities give rise to the variety of colors of beryl that can be found. Increasing alkali content within the silicate ring channels causes increases to the refractive indices and birefringence.

Beryl crystallizes hexagonally in the space group P 6 /mcc (space group no. 192) with lattice parameters a = 9.22 Å and c = 9.20 Å and two formula units per unit cell. The crystal structure of beryl consists of six-membered single rings with the structural formula [Si 6 O 18 ] 12−, which are concentrically stacked on top of each other in the direction of the c-axis and each rotated by 30°. Due to the concentric arrangement of the rings, open channels with a diameter of a few Ångströms are formed. The various impurities are interchangeably embedded in these hollow channels. The aluminum and beryllium ions are located between the rings, with aluminum being surrounded by six oxygen ions and beryllium by four oxygen ions. Therefore, aluminum and beryllium are also referred to as and coordination, respectively. 

Characteristics

Morphology

The crystal morphology of beryl is predominantly simple and is characterized by the hexagonal prism {10 1 0} and the terminal pinacoid {0001}. In addition, hexagonal-dipyramidal forms in the first and second positions {11 2 1} and {10 1 1} as well as the dihexagonal-dipyramidal full form (holohedry) are occasionally found. 

The habit can be short- to long-prismatic, with the prism surfaces often longitudinally striated. Occasionally, stem-like and granular to firm masses are also found. 

Physical and chemical properties

The melting point of beryl is 1650 °C. Beryl is insensitive to various acids and only slightly soluble in hydrogen fluoride (HF). However, it is sensitive to alkaline solutions and is therefore soluble in, among others, sodium hydroxide (NaOH, caustic soda) and potassium hydroxide (KOH, caustic potash). 

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