ZOISITE

( Fr- zoisite; Ger- Zoisit; Nor- zoisitt; Rus- )

ZOISITE, Ca₂Al₃(Si₂O₇)(SiO₄)(O,OH)₂.

A. Zoisite-ruby rock carving (height - 19 cm) made from Tanzania material. Betty Llewellyn collection. (© photo by Jeffrey A. Scovil)

DESCRIPTION: Two compact, massive, zoisite-rich rocks have found use as gemrocks: chromiferous zoisite and manganiferous zoisite. Neither of these two rocks, however, is the most used zoisite-rich rock for fashioing decorative items. That role falls to the zoisite-rich rocks in which red corundum is surrounded by green zoisite plus or minus a dark amphibole, usually referred to as hornblende, but in some records is reported as tschermakite (e.g., www-2.cs.cmu.edu). The zoisite of these rocks is typically granular and tends to appear sugary in most rough. The red corundum is typically a medium to low-grade ruby, which in some rocks exhibits fair to good hexagonal crystal outlines. The black amphibole commonly is manifest as speckles but in some rocks defines streaks that give the rock an overall gneissic appearance. The following properties are for the zoisite of these rocks:
    Colors - apple-green (zoisite, likely chromiferous but usually not so-designated )   or   rose-pink to purplish (thulite).
    H. 6 -6½
    S.G. 3.15 -3.37
    Light transmission - translucent to opaque
    Luster - pearly to subvitreous.
    Breakage - uneven to subconchoidal
    Miscellany - The red corundum grains in some of the ruby...zoisite rocks have corona like shell consisting of an off-white to yellowish material that, according to Chris Wright of Wright's Rock Shop, Hot Springs, Arkansas (personal communication, July, 2005) are "variations in the zoisite".

OTHER NAMES:

Anyolite is the name frequently applied to all gemrocks that consist largely of massive apple-green zoisite plus ruby-red corundum (i.e., medium or relatively low grade ruby) ± macroscopic hornblende. Ruby-zoisite, ruby in zoisite, ruby-in-zoisite and Tanganyika artstone are alternative names given this gemrock, especially in the market place.
Rosaline - marketplace name sometimes given thulite (q.v.)
Ruby-zoisite and ruby(-)in(-)zoisite, as just mentioned, are other designations used for anyolite, particularly in the marketplace. I suspect "ruby" is given primary billing for these rocks because of its likely appeal to potential buyers despite the fact that, considering the relative volumes of these components in these rocks, it would seem more appropriate for zoisite to be given top billing (see Figure A).
Tanganyika artstone - another name sometimes given to the green zoisite-ruby ... rock from Tanzania.
Thulite - name usually applied to the rose-pink to purplish, zoisite. Thulite that is massive, the common occurrence, is used as gemrock. The term thulite is used widely in scientific literature as the varietal name for any pink zoisite thought to be pink because of its manganese content, as well as in marketplace flyers etc.

USES: Anyolite has been carved, usually to exhibit both its red corundum and green zoisite constituents and their interrelationships to advantage -- see above Figure; some jewelry, usually relatively large pieces that display interrelations between major components; also spheres, eggs, hearts, pyramids etc.; and massage points and wands and "palm stones." Thulite has been used chiefly for fashioning cabochons and diverse ornaments. Both the green and pink more or less pure zoisites and saussurite (see REMARKS) have found use as jade substitutes.

OCCURRENCES: Metamorphic rocks: Zoisite-rich rocks as a group have had so many diferent origins suggested for them that it seems hardly worth repeating most of them here. Thulite, for example, typically as fracture fillings and as veins that transect several diverse, commonly metamorphic rocks, but several other occurrences have also been recorded. Most, if not all, high quality anyolite seems to occur as altered (metasomatized?) masses.

NOTEWORTHY LOCALITIES: Thulite -- Little Chief Mine, Alaska and Telemark, Norway. Anyolite -- near Longido, northeastern Tanzania (formerly Tanganyika).

REMARKS: Zoisite was named for the Slovenian noble, Sigmund (Žiga) Zois (1747-1819), Baron of Edelstein, whose interest in minerals led to his financing mineral collecting expeditions. It is said, however, that this mineral, first found in 1805 on the Svinška Planina (Sau-Alps) of Carinthia, Austria, was originally called saualpite and only later renamed zoisite. And, " While at first this may seem a travesty of scientific justice, we can at least rest assured that matters could have been worse. The name ... 'saualpite' ... Literally translated from the German, 'saualp' means 'female pig mountain.'"(/www.laketahoejewelers.com) Thulite was named for Thule, a former name for Norway, not, as many people believe, for Thule, Greenland; it was first described from Kleppan, Souland, Telemark, Norway. The name anyolite is apparently from the Masai (of Tanzania) word for green. Its type locality is near Longido, Tanzania.

Ruby-zoisite rocks are difficult fashion because of marked differences of hardness of their chief constituents -- i.e., On the Mohs hardness scale, zoisite and hornblende (or tschermakite) have hardnesses about about 6½, whereas corundum has a hardness of 9. In any case, carvers usually try to fashion these rocks to use the colors artistically and, in most cases, to emphasize the red corundum-rich parts of these rocks.

Mineralogically, zoisite is a member of the epidote group, the other members of which are clinozoisite, epidote per se, piemontite, and allanite. Thulite is the only variety of zoisite that commonly occurs as compact masses used as such as gemrock. As already mentioned, the so-called ruby-zoisite gemrocks include large percentages of minerals other than zoisite. Epidote per se is a specific, though commonly minor, constituent of the gemrock unakite (see UNAKITE entry) and also of Bowesite, Okkolite and the unnamed epidote-quartz rock, all of which are included in APPENDIX A. In addition, saussurite (named for the famous Swiss naturalist, explorer and inventor Horace Bénédict de Saussure), which is made up largely of microscopic mixtures of zoisite and/or epidote plus a sodium-rich plagioclase feldspar (typically albite or albit-oligoclase), has been used as a jade simulant under names such as Swiss jade and Nanyang jade (see JADE entry).

Tanzanite, another variety of the mineral zoisite has found wide acceptance as a gemstone. It, however, is a macrocrystalline, transparent, bluish purple variety that is properly called a gem-mineral rather than a gemrock. Nontheless, it seems noteworthy here that soon after the September 11th (2001) attacks, word was spread around the marketplace that sales of tanzanite helped fund Osam bin Laden and the Al-Quaeda network. And, as a result, several jewelers, especially in the United States, imposed a boycott on further imports of the gem, and some of them even removed tanzanite-bearing jewelry from their active inventories. Subsequently, however, the U.S. State Department said that no evidence appeared to tie sales of tanzanite to funds supporting the Al-Quaeda, and many jewelers lifted their boycott (etc.).

REFERENCES: No general reference. Abrecht, 1981. Gübelin, 1969. Keller, 1992.

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