Zektzerite

The mineral zektzerite is a member of the tuhualite group and was first found in 1966 by Seattle mineralogist Benjamin Bartlett "Bart" Cannon. It was discovered in the Willow creek basin below Silver Star mountain in miarolitic cavities within the alkaline arfvedsonite granite phase of the Golden Horn batholith, Okanogan County, Washington. It is named for Jack Zektzer (born 1936), mathematician and mineral collector of Seattle, Washington.

The mineral was misidentified as alkali beryl (morganite) at that time. Subsequently, in September, 1975, additional specimens of the mineral were found in a "float boulder" (a glacial erratic, or dropstone) on the north side of Kangaroo Ridge at an approximate elevation of 6,500 feet (2,000 m); it was recognized that the material was not beryl.

Zektzerite

General

Category Inosilicate

Formula LiNa(Zr,Ti,Hf)Si6O15

IMA symbol Zek

Strunz classification 9.DN.05

Crystal system Orthorhombic

Crystal class

Dipyramidal (mmm)

H-M symbol: (2/m 2/m 2/m)

Space group Cmca

Identification

Formula mass 529.66 g/mol

Color Colorless to pink, cream, or white; commonly zoned

Crystal habit Stout pseudohexagonal prisms

Cleavage {100} and {010} perfect

Mohs scale hardness 6

Luster Vitreous to pearly

Streak White

Diaphaneity Translucent to transparent

Specific gravity 2.79

Optical properties Biaxial (-)

Refractive index nα = 1.582 nβ = 1.584 nγ = 1.584

Ultraviolet fluorescence Light yellow

Etymology

Zektzerite was first discovered at Washington Pass near Golden Horn in Okanogan County, Washington. First described in 1977 by Pete J. Dunn, Roland C. Rouse, Bart Cannon, and Joseph A. Nelen, who named the mineral after Jack Zektzer (born 1936), who provided the mineral to the scientists for their research. 

Classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz, zektzerite belonged to the mineral class of “silicates and germanates” and there to the division of “chain silicates and band silicates (inosilicates)”, where it formed an independent group together with pellyite and tuhualite.

The 9th edition of Strunz's mineral classification, valid since 2001 and used by the International Mineralogical Association (IMA), also classifies zektzerite in the class of "silicates and germanates" and within 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 6-period double chains," where it forms the unnamed group 9.DN.05 together with emeleusite and tuhualite.

Dana's mineral classification also classifies zektzerite in the class of "silicates and germanates," but within the division of "chain silicates: double unbranched chains, W=2." Here, it is found together with tuhualite and emeleusite in the "tuhualite group P=6" with system number 66.03.04 within the subdivision " chain silicates: double unbranched chains, W=2 with chains P>2."

Properties

Synthesis: by fusion of Li2CO3, Na2CO3, SiO2, ZrO2. The resulting material has a brilliant blue-white fluorescence under short-wave ultraviolet light.

Crystal structure

Zectzerite crystallizes orthorhombic in the space group Cmce (space group no. 64) with lattice parameters a = 14.33 Å, b = 17.35 Å and c = 10.16 Å and 8 formula units per unit cell. 

Chemical characteristics

It is a silicate of sodium, lithium, and zirconium. The molecular structure is that of amphiboles, with chains of double silica tetrahedra with period six. 

In addition to the elements in its formula, it usually contains impurities such as titanium and hafnium.

Formation

It forms as a rare secondary mineral filling miarolitic cavities and as isolated grains in alkaline syenite rocks, also in a granite with riebeckite.

It is usually found associated with other minerals such as: quartz, microcline, aegirine, riebeckite, astrophyllite, zirconium or elpidite.

Occurrence

Zektzerite is a mineral of agpaitic granites with arfvedsonite. It occurs with smoky quartz, microcline, okanoganite, sogdianite, astrophyllite, and zircon. It is found in cavities as euhedral crystals in the agpaitic-granite phase of the Golden Horn batholith, Okanogan County, Washington. It also occurs in blocks of pegmatite as rock-forming grains in a moraine of the Dara Pioz glacier in northern Tajikistan; in the Del Salto pluton in Aysén Province, Chile; as euhedral crystals at Virikkollen, Haneholmveien, Sandefjord, Norway; Ampasibitika, Ampasindava Peninsula, Madagascar; and as gemmy crystals up to 3 cm from Mt. Malosa Malawi.

Use

For commercial use as a raw material or gemstone, zectzerite is too rare and, due to its perfect cleavage, too fragile. However, it is occasionally cut into various shapes for collectors. 

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