TIGER'S-EYE & HAWK'S-EYE

( Fr-oeil de tigre & oeil de faucon; Ger- Tiger-auge & Falkenauge;
Nor-tiger(-)øye & hauk(-)øye/falk(-)øye; Rus-

)

TIGER'S-EYE and HAWK'S-EYE

A. Tiger's-eye round cabochon (diameter - 3.7 cm). (© photo courtesy www.mysticmerchant.com)

B. Hawk's-eye "teardrop " (1.9 x 3.3 cm) from South Africa. Being a fan of Northern Lights (aurora borealis), I especially like this photograph of this stone. (© photo courtesy topgems.homestead.com)

C. "Tricolor" cabochon (3.76 x 2.8 cm) that exhibits both Tiger's-eye and Hawk's-eye, as well as reddish zones. Rough from Cape Province, South Africa. (© photo courtesy topgems.homestead.com)

D. Pietersite (height - ~ 5.1 cm) from from Namibia (formerly South-West Africa). (© photo courtesy topgems.homestead.com )

E. Fiber optics sphere (diameter - 5 cm). A possible simulant for hawk's-eye. (© photo courtesy www.wehug.com)

DESCRIPTION: The following descriptive material differs in form from that given for most of the other gemrocks because two materials are included in this entry. This approach seems warranted because both are formed by the replacement of crocidolite (asbestiform riebeckite) by silica (quartz). Although Tiger's-eye is listed first in the heading -- because it is more widely known -- descriptive information about Hawk's-eye precedes that for Tiger's-eye because the general consensus (not without alternatives -- see REMARKS) is that Hawk's-eye is a precursor of Tiger's-eye. And, these are followed by properties common to both.

Hawk's-eye consists of closely packed parallel crocidolite fibers that have been permeated and/or partially replaced by virtually colorless microcrystalline quartz. Crocidolite is the name applied widely to asbestiform (i.e., fibrous) riebeckite, which is an amphibole.
    Color - diverse blue hues, commonly grayish, less commonly greenish, typically striped
    H. crocidolite - 6; quartz - 7
    S.G. 3.0-3.6

Tiger's-eye consists largely of microcrystalline quartz pseudomorphs after hawk's-eye. In tiger's-eye, however, the precursor crocidolite fibers have been altered (chiefly oxidized) to hydrous iron oxide ("limonite"), and at least some of the so-called fibers are cavities or cavity fillings in some specimens. In addition, the pseudomorphism of some specimens has been shown to have involved only partial replacement.
    Color - various shades of golden or honey yellow and various brown hues, typically roughly striped
    H. (effective hardness) 6.5 - 7
    S.G. ~ 2.65 - 2.9.

Hawk's-eye and Tiger's-eye --
    Light transmission - subtranslucent to opaque
    Luster - a silky sheen that is improved markedly by cutting and polishing
    Breakage - subconchoidal to irregular
    Miscellany - chatoyant in a broad sense -- this is aptly described by Webster (1986) as follows:   “A polished surface ... when turned towards the light often shows a series of lustrous bands alternating with bands of duller colour which show little silkly lustre. The beauty of the effect is enhanced by the fact that the fibres are not always perfectly straight; they may be curved and often have a sharp bend or twist at a certain place. [And,] a change in the incident light results in a reversal of the conditions, the dark bands becoming lustrous and the lustrous bands becoming dark.”; magnetic -- many of these gemrocks are attracted to a magnet because they commonly include bands (i.e., zones), which are typically thin and discontinuous, of magnetite.

OTHER NAMES: First of all, a brief summary of a nomenclature nightmare: Hawk's-eye is recorded in English-language literature as Hawk Eye, Hawk-eye, Hawkseye, and Hawk's Eye; Tiger's-eye appears as Tiger Eye, Tiger-eye, Tigereye, Tigerseye, and Tiger's Eye, and also as Tigerite. The versions used in this document follow use in current USGS and GIA publications.

The following names include terms that are no longer used or unfortunately applied (luckily not widely), as well as terms that have rather good standing, at least in the marketplace.

Binghamite (cuyunite) - red, brown, golden yellow and/or buff colored chalcedony, with the colors dependent up the presence and abundance of included goethite fibers; some of this chalcedony is chatoyant, and consequently the rock has been described more elaborately as “an iron heavy rock that has inclusions of the familiar tigereye fibers...[whose] chatoyance is more subtle than in other varieties ... [and] Large pieces containing a high percentage of tigereye are rare.” (Hill, 1978). It was named after Bill Bingham, a lapidarist from St. Paul, who discovered the material on mine dumps of the area in 1936. (topgems.homestead.com) The alternative name is based on the occurrence of this material in the Cuyuna iron range near Crosby, central Minnesota.
Blue tiger's-eye - name sometimes given hawk's-eye.
Bull's eye (or ox-eye) - terms sometimes given tiger's-eye having a relatively dark mahogany-red as its chief color. This application of these designations is unfortunate; among other things, both terms have also been used for other gem materials such as labradorite (anorthosite).
Brockman tiger-eye - name sometimes given to tiger's-eye from Mt. Brockman area of northwestern Western Australia.
Cat's eye quartz - name sometimes given tiger's-eye in the 18th century. This use, now abandoned, is not applicable because the so-called cat's eye effect, which a number of minerals exhibit when cut appropriately, has a widely accepted meaning that does not describe the chatoyancy of most hawk's-eye or tiger's-eye; furthermore, as a noun, the term is applied widely to the greenish gem variety of chrysoberyl.
Crocidolite (or "silicified crocidolite") - the mineral name alone is applied rather frequently, especially in the UK, to tiger's-eye (and hawk's-eye?).
Eagles eye - see pietersite.
Falcon's eye - term sometimes given hawk's-eye, especially in Germany (Falkenauge).
German tigereye - name sometimes applied in the marketplace.
Golden Chinese tiger's eye - marketplace name sometimes given to tiger's-eye from China.
Griqualandite - term formerly used as an overall synonym for tiger's-eye or applied to only its yellowish "layers." This name, no longer in vogue, was based on the occurrence of tiger's-eye in the Asbestos Mountains, west of Griquatown, South Africa.
Harlequin stone - name applied to "artificially [multi-?] colored crocidolite" (Hart, 1927)
Hungarian cat's-eye - "vague term" that includes "grey varieties, and paler types which have been stained in a number of unlikely colours, . . . sometimes seen in cheap jewellery" ( Anderson, 1980).
Marra mamba - "considered the Rolls Royce of all tiger eye by many collectors and lapidarists ... [from] the Hamersley Ranges of the Pilbara region in Australia ... [where it has been found in only two deposits] ... the 'true' marra mamba, a very rare type with reds, blues, yellow gold and greens! ... has been mined out for nearly twenty years." ( topgems.homestead.com )
Ox-eye - see Bull's eye.
Pietersite - a breccia made up largely of hawk's-eye and/or tiger's-eye plus or minus sporadic zones of virtually colorless quartz. This gemrock was discovered in 1962 in northern Namibia (formerly South-West Africa) by Sid Pieters, a prospector (Craig Gibson, personal communication, 2002). A similar rock, but typically with fragments that include markedly red- and golden red zones, was found in 1993 in Nangang, Hunan Province, China, and called Chinese pietersite or "eagles eye" (see Figure D).

Pseudocrocidolite - probably the most nearly correct name for tiger's-eye, and used in some literature -- e.g. Webster (1986).
Red tigereye - name given to tiger's-eye the colors of which have been changed by heating, which apparently oxidizes the iron, thus turning it red.
Rodusite - Russian tradename name hawk's-eye.
Silkstone - a variety of binghamite. "When enough tigereye is present to dominate the stone, the material is known as silkstone." (Hill, 1978).
Strawberry tigereye - name given tiger's-eye that as the result of having been heated either naturally or artificially has taken on a reddish color.
Tiger's eye matrix - "quartz-lignite (sic) aggregate [with] . . . gold-yellow highlights and sometimes scenic markings" from an unreported locality (Schumann,1977?, p.202).
Tiger's eye quartz - term sometimes applied to tiger's-eye.
Tiger iron - name given, especially in the marketplace, to a red, hematite-rich microcrystalline quartz rock "similar to tiger's eye" from the banded iron formations near Port Hedland, Western Australia (Pough, 1996).
Wolf's-eye (or wolf's-eye stone) - term sometimes given material the color of which is intermediate between those of typical hawk's-eye and typical tiger's-eye
Zebra tiger's eye - term applied, albeit infrequently, to tiger's-eye exhibiting sporadic blue tones, apparently because some of the original crocidolite is still present.

USES: Both tiger's-eye and hawk's-eye are used in jewelry -- usually as cabochons, but also as small spheres, diverse prisms (some with rounded edges), faceted forms, small carvings (scarabs, cameos, intaglios, etc.), and even tumbled chips. They also have been carved and fashioned into articles such as boxes, cane heads, eggs, hearts, obelisks, pyramids, snuff bottles, spheres and diverse figures. In addition, especially in the past, they were also used as eyes -- i.e., set into the eye sockets -- of carvings fashioned from other gemrocks, shell and wood.

OCCURRENCES: As already noted, hawk's-eye is asbestiform crocidolite that has been so-to-speak permeated or partially replaced by silica. The precursor crocidolite asbestos -- at least that at the well-known tiger's-eye locality, west of Griquatown, South Africa -- consisted of fibers ranging up to a few centimeters long and only 0.001+ mm in diameter (Bauer and Schlossmacher, 1932, 673.). According to a summary given by Deer, Howie and Zussman (1992), tiger's-eye -- and, I suspect they also would include hawk's-eye -- occurs "in iron formations of South Africa and western Australia where it occurs in seams conformable with the bedding of the ironstone. The composition of the crocidolite is closely comparable with that of the ironstone . . . crystallization of the amphibole, initially in the form of massive riebeckite, occurred with little or no addition of material and under conditions of moderate temperature and pressure consequent on the burial of the ironstones to moderate depths. . . . transformation of the riebeckite to the fibrous crocidolite may [have] result[ed] from the instability of the massive riebeckite during a period when the ironstones were subjected to shearing stress." Amstutz and Hälbich Stellenbosch (1992), however, have concluded that the "pseudomorphism of tiger's eye is of near-surface origin...[and may] be considered a specific type of silcrete formation." (See also Sinclair, 1941) And, more recently, Heaney and Fisher (2003/2004) have concluded that the long and widely held idea that these gemrocks are quartz pseudomorphs after asbestiform crocidolite is incorrect; they present data derived from their investigation of specimens that they interpret to represent synchronous mineral growth of chiefly quartz and crocidolite as a consequence of crack-sealing, vein-filling processes. Whatever the correct origin(s?), at least in South Africa, where the gemrock material comprises relatively thick slabs, tiger's-eye appears to have been formed from hawk's-eye as the result of the breakdown -- chiefly oxidation -- of crocidolite, with preservation of the original fibrous nature of the overall mass. Furthermore, it seems worth repeating here that "In some tiger-eye the crocidolite has been wholly destroyed, leaving hollow tubes that may be partly filled with hydrated iron oxide" (Frondel, 1962).

NOTEWORTHY LOCALITIES: The most important source of both tiger's-eye and hawk's-eye is South Africa. Commercial quantities have also been recovered from India; Myanmar (formerly Burma); Sri Lanka (formerly Ceylon); the Hamersley range of the Pilbara region and Mt. Brockman, West Australia; Brazil; and California. Pietersite, as mentioned, comes from Namibia (formerly South-West Africa), and from Nangang, Hunan Province, China. Localities for some of the varieties that have been given special names are given under the OTHER NAMES subheading.

REMARKS: The names given these gemrocks were apparently based on their chatoyancy, which roughly resembles the eyes of tigers and hawks. I have been unable to date to find the first application of these terms to these gemrocks.

Although it is generally thought that these gemrocks are only rarely enhanced, Anderson (1980) reports that "grey varieties, and paler types . . . have been stained in a number of unlikely colours"; Webster (1986, p.89) notes, “It appears that many pseudocrocidolite cabochons are stained –vivid greens, blues and blacks, which are obviously stained, have been seen. This staining may be carried out in a similar manner to that used for staining agates.”; [and] as already noted under the OTHER NAMES subheading, Hart (1927) lists the name "Harlequin stone" as a name applied to "artificially colored crocidolite." Also, as already mentioned, some tiger's-eye has been heated to produce deep red and brownish-red tiger's-eye; a procedure is outlined on the web site topgems.homestead.com . And, some hawk's-eye and tiger's-eye have been acid treated to produce what is marketed as "grey tiger eye." In addition, according to information given on the web site www.minerals-n-more.com: "Soon after Tiger Eye's discovery in the late 19th century [this date is, by the way, not correct!], Idar-Oberstein lapidaries discovered they could bleach tiger-eye to an evenly colored light yellow . . . By using either hydrochloric or oxalic acid. [And,] When properly oriented and cut, this material could yield a sharp cat's-eye stone . . . reminiscent of 'real' cat's-eye." It is also reported (topgems.homestead.com) that open spaces in Pietersite and bighamite stones have sometimes been "filled with wax, super glue or opticon in the last steps of sanding and polishing."

Some jewelers and other marketers recommend cleaning these gemrocks with only a polishing cloth -- i.e., they say these gemrocks should not be submitted to such things as alcohol, steam, or an ultrasonic gem cleaner. Furthermore, they frequently (prudently!!) direct attention to the fact that when struck, these stones are more likely than many other gem materials to chip or break.

Several praiseworthy virtues have been attributed to these stones. Although I have made a point not to give the purported attributes for most gemrocks, a few are given here as an example of the types of things that one can find recorded for just about all gemstones (both gem minerals and gemrocks): So far as physical and mental health, tiger's-eye is said to be "a good general tonic [for] hypochondria, eye diseases, stubbornness, spleen, pancreas, digestive organs, blood purification, unwanted emotion"; to "be an aid to the treatment of ulcers. . . . [and] to improve night vision." (www.crystalbeauty.co.nz) Elsewhere it is noted, for example, that "Tiger's eye is closely attuned to earth energies, but the shimmering, eye-catching yellow highlights are linked to the sun. Thus tiger's eye is a bridge between earth and sky, a link or tool representing a balance between the physical and the spiritual. [-- that is,] Its energies promote psychic ability by connecting the physical earth aspects of self with the non-physical spiritual aspects. . . . [Also,] As a link between Father Sky and Mother Earth, tige'sr [sic] eye can help balance the male and female energies that are within us all. [Indeed,] This stone's influence is one of harmony between yin and yang., and it's energies can help us to achieve this same balance (www.crystalbeauty.co.nz). In addition, "Tiger's Eye . . . helps us recognize the resources within ourselves and [how to] use those resources for the attainment of our dreams. [And,] It helps us judge a situation and determine how best to approach it." (??). Furthermore, "Tiger Eye can help you become practical as well as more grounded. It has been used to stimulate wealth and enhance the stability to maintain wealth." (www.blacktassel.com). Indeed, I have even been told that it may even be programmed (how was not revealed) to help one see different possibilities before acting. etc., etc. -- These, in my opinion, are examples of fabricated marketing ploys, but I have been cautioned "who are you to make such an assumption(?). However, is it not interesting that even the recently discovered Pietersite has been assigned such attributes: For example, it is "said to contain the 'keys to the kingdom of heaven,' dispelling illusion and assisting one in the recognition of the beauty of the soul. . . .[; to] exhibit[s] an energy conducive to the actualization of the loving characteristics of the "brotherhood" of humanity. ...[; to] bring[s] the potential of the individual to the perfection of the source of all being, stimulating dignified power and loving guidance. . . . [; and to] promote[s] loyalty to the self and to the ultimate experience of life. -- [And, it ] can be used to stimulate the pituitary gland to provide the proper regulation of the other endocrine glands and to produce, in the proper quantity, the hormones concerned with growth, sex, metabolism, blood pressure, and body temperature." (www.vjdesigns.com). Yikes!!! Also, for what it may mean or be worth, "Tiger's Eye is a warm stone which is recognised as slightly masculine... [and] a good stone for those born during The Moon of Growth [i.e., under the zodiac sign of Taurus] - (20 Apr - 20 May)." (www.crystalbeauty.co.nz).

In some circles, tiger's-eye is considered to be the gemstone for the ninth wedding anniversary.

SIMULANTS:

Arizona tiger-eye - asbestiform, translucent, amber-colored serpentine that exhibits a fine chatoyance. The name is why I include it here -- I do not know of its ever been marketed as tiger's-eye per se. - [ inferior hardness].

California tiger's eye - "silica-impregnated, white-to buff-colored, massive fibrous tremolite ... [from] Iowa Hill in Placer County. It is sometimes called Placer County tigereye. ... It has a chatoyance similar to silkstone. (topgems.homestead.com) In the same way as the above listed simulant, the name is the reason I include it here -- I do not know of its ever been marketed as tiger's-eye per se. - [Appearance suffices.].

Fiber Optics - certain shades of blue and golden brown fiber optics fashioned as cabochons used in costume jewelry and for curios -- e.g., spheres marketed as scrying balls (i.e., so-called “crystal” or future-predicting balls) -- roughly resemble hawk's-eye and tiger's-eye, respectively. - [So far as I have been able to determine, the fiber-optics used for these purposes consist of strands of glass and/or plastic; consequently, their overall hardnesses are less than the effective hardness of either hawk's-eye or tiger's-eye; in addition, to me they have an overall artificial appearance (see Figure E).].

"Fire jade - looks like tiger's eye, mainly opal" - the preceding "bald statement" appears on www.gemscape.com/html/misnomer.htm. I have found no additional information about this material.

***Forsterite (Mg-olivine) - this synthetic olivine has been sold as "rodusite" (Federov, 2002). - [said to exhibit melt features].

Serpentine - asbestiform serpentine veins within massive serpentine(?) has been marketed as pietersite (or Arizona pietersite). [resemblance is not that good; fibers of asbestiform veins are virtually perpendicular to their marginal surfaces; S.G. is 2.50-2.58 versus the 2.67-2.74 of true pietersite (Hu and Heaney, 2010) ].

***Tiger's eye soaprock® - This glycerin soap consists of layers of browns, golden yellows and dark gray, the thicknesses and arrangements of which roughly resemble tiger's-eye (www.artisticdelights.com/tigerseye). - [Appearance suffices to distinguish it from tiger's-eye.].

REFERENCES: Webster, 1986. For Pietersite: Hu and Heaney, 2010 & 2010a.

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