Goshenite in gem

Goshenite is a colorless gem variety of beryl. It is called the mother of all gemstones because it can be transformed into other like emerald, morganite, or bixbite. Goshenite is also referred to as the purest form of beryl since there are generally no other elements present in the stone. The gem is used as imitation for diamond or emerald by adding colored foil on it.

Goshenite (gem)

General

Category beryl

Formula Be3Al2(SiO3)6

Identification

Color Colorless

Name

Goshenite is named after Goshen, Massachusetts, United States, where it was first found. It is also known as white beryl or lucid beryl.

Value and treatments

Goshenite is not popular in the jewelry industry because of its colorlessness and lack of brilliance, luster, or fire. It is also inexpensive due to the fact it is abundant.

Although the gem value of goshenite is relatively low, it can be colored yellow, green, pink, blue, and in intermediate colors by irradiating it with gamma rays and bombarding it with neutrons from nuclear reactors and radioactive materials. The resulting color depends on the content of Ca, Sc, Ti, V, Fe, and Co impurities.

Occurrence

It is most commonly found inside granite. It can also be found in metamorphic rocks. Goshenite can be found in countries like China, Canada, Brazil, Russia, Mexico, Pakistan, the United States, and Madagascar.

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Already in the outdated 8th edition of the mineral classification according to Strunz, beryl belonged to the mineral class of “silicates and germanates” and there to the division of “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 (Al 2 O 3), 14% beryllium oxide (BeO) and 67% silicon dioxide (SiO 2).

Natural beryl can contain various impurities, including rubidium oxide (Rb 2 O) and cesium oxide (Cs 2 O). 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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