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NaCa[B5O6(OH)6] · 5H2O
Colourless, white, grey ...
Vitreous, Silky
Named after George Ludwig Ulex (1811-1883), German chemist, who first correctly analyzed the species.
Most specimens of Ulexite are fibrous in nature. Most of the times the fibers are intergrown into felt like aggregates. The first commercial production of borates here in the US in dry/moist lake beds like Teals Marsh in Nevada and later in Death Valley, California where Ulexite was skimmed from the surface of the ground, much of it in the form of "cotton balls" which were then processed into borax and other borate products. These felt like aggregates are not of much interest to collectors because their common admixture with mud makes them unattractive. Sometimes, Ulexite takes other forms that are of more interest to collectors and those are show below in pictures of specimens from Boron, California. Most familiar to collectors is the kind of Ulexite that is popularly called TV rock because of its natural fiber optic character. Less well known forms are the acicular variety that can make for spectacular specimens and the form that is called "clam shell" Ulexite. To the best of my knowledge these forms of Ulexite are not found at other borate deposits. Ulexite was the main ore along with Colemanite for years until the discovery of crystallized borax at Boron, California and after that it was forced into a secondary role as a sometime ore for borates.

Collectors find the acicular form of Ulexite to be the most attractive, but most are not even aware that it exists. The very thin radiating needles of Ulexite are very delicate and great care must be taken to protect them from damage. They are found growing in cavities in the ore, sometimes growing on sparkling white or tan Colemanite crystals. They can make stunning specimens, but great care must be taken in collecting and storing them. See pictures 3 & 4 above. Most of the good specimens that have been collected have gotten dirty, damaged and ultimately thrown away. The mining process also weighs in strongly against the recovery of these delicate specimen. The Ulexite is found in the top most layer of the borate deposit just above the Borax which is the main ore of interest. To mine the deposit shafts were dug down through the Ulexite and Colemanite layer to access the Borax. At one time the underground mine at Boron was the largest underground operation in California with more than 200 miles of tunnels and stopes. A few specimens of Ulexite were found during the shaft digging process or whenever the underground workings intersected the Colemanite/Ulexite ore above the Borax. Eventually economics dictated that the deposit be open pitted. The sandy overburden was removed and below that the borates in the distinctive bluish tan mud of the deposit was encountered and this top layer was particularly rich in Ulexite and Colemanite. This material was dug and removed to long term borate storage dumps separate from those containing the sandy overburden. There it sits waiting for the day when borax runs short and it will be profitable to process the borates in these dumps into borate products. When this top most layer of borates was encountered, thousands of tons of Ulexite and Colemanite specimens were exposed and some of the miners spent as much time collecting them as they could. Some of the operators of the big bull dozers told stories about sinking their big ripper blades into the ore and listen to the sounds of the brittle pocket riddled rock crackled and popped as chunks of crystal lined specimens were exposed behind the machines they were driving. This was in the late 1950's and work rules and safety procedures were often only given lip service. Some of the miners would collect what they could in their spare time and sometimes after work. The drilling and blasting foreman Howard Pomptier developed an interest in minerals and it was his job to check the benches after each blast to see if there might be any problems from un-detonated explosives. For a mineral collector, this was the best job in the world. In the early days some collectors were even able to collect in the open pit mine, but soon they were kept out of that, and were relegated to working the dumps, which were still pretty good. When I worked there in the early 60s I could still collect on the dumps, but had to be very careful that one of the big mine haul trucks didn't dump 150 tons of rocks on me as I was collecting on the slope of the dump below. But collecting on the dumps was not very productive compared to the specimens you could collect in the open pit after a blast. I soon found out that I could buy much better specimens from the miners than I could dig on the dump. Today, even the dumps are off limits to collectors.

In addition to the damage delicate Ulexite specimens suffer from the bench blasting, modern safety regulations do not allow anyone to get within 30 feet of a bench wall. If a bench is 30 feet high you must stay 30 feet from the wall. The blast pile is scooped up by big diesel electric shovels, placed in huge 200+ ton mine haul trucks and taken out to the dump and added to the growing mountain of the borate dumps at Boron. From time to time specimens are encountered, but in effect, no one is allowed to get near them and collect specimens. There are occasional exceptions but in reality the specimen production at Boron is pretty well shut down, because of the restricted access to the specimens during the mining process.

In addition to the acicular "bunnies tale" Ulexite, the deposit also produced a form of Ulexite that is know to collectors as optical Ulexite or more commonly TV rock. See pictures 5, 6, 7, 8, 9 & 10 above. When it was formed the thin acicular crystals of Ulexite grew next to each other in a parallel fashion and when chunks of this massive material is cut perpendicular to the long axis of the crystals, the resulting material demonstrates a fiber optic effect. When a piece of cut and polished Ulexite is placed flat on a surface of printed material, the printed material appears to be transmitted to the top of the piece, sort of like an image on a TV screen. It is a fascinating optical effect and any amount of it can be collected, cut and polished and sold to rock shops. Most of Ulexite found at the borate deposit at boron (99%+) of the material is if a fibrous intergrown nature demonstrated by pictures 13, 14 & 15 above, but sometimes veins of Ulexite with parallel growing fibers is encountered. Some times hundreds of pounds of this stuff can be picked up from the blast piles and the dump. But a great deal of good TV rock is off limits to the one individual the mine management allows in to collect it. He must pick up what few pieces he can from areas that are not set as off limits by safety regulations. Small pieces of an inch by an inch are commonly available, but larger pieces are sought after by collectors and schools for demonstration purposes. The old timers would talk about the big foot long pieces of TV rock that they once had or saw, but 50 years of experience have taught me that these were just stories and that there was never such thing as a foot long piece of optical Ulexite. Most of this compact form of Ulexite is found mixed with mud that prevents light being transmitted very far or that although the rough material looks like it might produce fine optical material, when you cut and polish it, you find that the fibers are really not very parallel after all and that also limits the length of optical transmission. I think about the longest piece of TV rock I have ever seen is about 6 inches, though I have seen many large chunks that gave promise that they might produce the legendary foot long piece. They have never panned out. Because of optical Ulexite's nature with all the crystals growing parallel to each other, fine high domed cabochons can be cut from it which show a fine "cats eye" effect. The problem is that this form of Ulexite is extremely heat sensitive and often full of cracks from the bench blasting in the mine. Because of this extreme heat sensitivity the material must be worked under a continual spray of water to keep it cool. The material is "butter" soft, and when making cabochons, you need to use a worn out 600 grit sanding paper to do the final shaping on the stones. A fresh 600 grit sanding paper will remove material so quickly from the stone that you can't round it properly and develop too many flat spots. You also have to finish it on a rag buff with tin or cerium oxide but also with a continuous spray of water. Even then, you will sometimes thermally crack the stone. These stones show a wonderful cats eye, but in time, the Ulexite will react with the atmosphere and the surface of the stone will become clouded and you must polish it again.

Another interesting form of Ulexite is the clam shell variety. See picture 11 above. This type of Ulexite if sometimes found at the top of the borax ore body in the blue/green/tan shale. Most of these specimens were collected from the roof of the big mine tunnel that opened into the old underground mine from the bottom of the open pit. You don't often see them offered for sale, not that there is any great demand for them. You can see that they would not compete very well for a collectors interest compared to a nice gemmy bi colored tourmaline.

Some times in the mud of the deposit you can find Ulexite pseudomorphs after Borax. See picture twelve above. Only a mother can love a specimen like this. Note however the "dirt" on the specimen. This is the typical blue/tan/green mud that is so distinctive of many matrix specimens from Boron. Often when you see this "mud" you know the specimen is from Boron, because the other borate deposits in the US do not have this color "mud". It may also be distinctive in separating it from specimens from the deposits in Turkey and South America. There is a surprising amount of arsenic in the deposit and it is most commonly manifested by the appearance of red Realgar that is commonly found mixed with Ulexite. It never occurs in big crystals, but sometimes very nice micro crystals of Realgar are found. Left for any length of time exposed to sun light, the Realgar quickly alters to yellow/orange Pararealgar. Sometimes sharp shiny Tunellite crystals are found growing with acicular Ulexite, but in these cases, the Ulexite is brushed aside to expose the Tunellite crystals. These are quite rare. See Best Minerals/Ulexite on Mindat for more pictures.
Rock Currier 2015

Visit for gemological information about Ulexite.

Classification of Ulexite

Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"

E : Pentaborates
A : Neso-pentaborates

5 : Pentaborates

9 : Borates
3 : Borates of Ca and Sr URL:
Please feel free to link to this page.

Type Occurrence of Ulexite

Year of Discovery:
Geological Setting of Type Material:
Playas in a desert region.
Associated Minerals at Type Locality:

Occurrences of Ulexite

Geological Setting:
Arid regions. In salt playas and desiccated saline lakes.

Physical Properties of Ulexite

Vitreous, Silky
Diaphaneity (Transparency):
Colourless, white, grey with included clays.
Hardness (Mohs):
Perfect on {010}; on {110} good; on {110} poor.
Fracture uneven across fibers.
1.955 g/cm3 (Measured)    1.955 g/cm3 (Calculated)

Crystallography of Ulexite

Crystal System:
Class (H-M):
1 - Pinacoidal
Space Group:
Cell Parameters:
a = 8.816(3) Å, b = 12.87Å, c = 6.678(1) Å
α = 90.25°, β = 109.12°, γ = 105.1°
a:b:c = 0.685 : 1 : 0.519
Small nodular, rounded, or lens-like masses; loose at times (termed "cotton balls"), comprised of acicular crystals. Fibers may be radially arranged or randomly oriented towards the centers of the masses and arranged in parallel position at the periphery. Botryoidal crusts or randomly oriented fibers. Compact veins with a parallel fibrous structure. Distinct crystals rare, greatly elongated [001] (Palache et al (1951) Dana's System of Min.: 345).
Polysynthetic, common in massive aggregates and crushed fragments. Several twin laws apply: 1. Polysynthetic on {010} and {100}; 2. {340} or {230} less certain, and others of a more complex nature.
X-Ray Powder Diffraction:
Image Loading

Radiation - Copper Kα
Data Set:
Data courtesy of RRUFF project at University of Arizona, used with permission.

Optical Data of Ulexite

Biaxial (+)
RI values:
nα = 1.491 - 1.496 nβ = 1.504 - 1.506 nγ = 1.519 - 1.520
Measured: 73° to 78°, Calculated: 68°
Max Birefringence:
δ = 0.028
Image shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:

Chemical Properties of Ulexite

NaCa[B5O6(OH)6] · 5H2O
All elements listed in formula:

Relationship of Ulexite to other Species

6.EA.05SborgiteNa[B5O6(OH)4] · 3H2O
6.EA.05LeucostauritePb2[B5O9]Cl · 0.5H2O
6.EA.10SantiteK[B5O6(OH)4] · 2H2O
6.EA.10Ramanite-(Rb)Rb[B5O6(OH)4] · 2H2O
6.EA.10Ramanite-(Cs)Cs[B5O6(OH)4] · 2H2O
6.EA.15Ammonioborite(NH4)2[B5O6(OH)4]2 · H2O
9.3.4UralboriteCa2[B3O3(OH)5 · OB(OH)3]
9.3.6OlshanskyiteCa2[B3O3(OH)6](OH) · 3H2O
9.3.8KorzhinskiteCa(B2O4) · H2O
9.3.9TyretskiteCa2B5O9OH · H2O
9.3.12InyoiteCa(H4B3O7)(OH) · 4H2O
9.3.13GoweriteCa[B5O8(OH)][B(OH)3] · 3H2O
9.3.14ColemaniteCa[B3O4(OH)3] · H2O
9.3.15PentahydroboriteCaB2O(OH)6 · 2H2O
9.3.16HexahydroboriteCa[B(OH)4]2 · 6H2O
9.3.17MeyerhofferiteCa2(H3B3O7)2 · 4H2O
9.3.18PriceiteCa2B5O7(OH)5 · H2O
9.3.19GinoriteCa2B14O20(OH)6 · 5H2O
9.3.20ProbertiteNaCaB5O7(OH)4 · 3H2O
9.3.22HydroboraciteCaMg[B3O4(OH)3]2 · 3H2O
9.3.23InderboriteCaMg(H3B3O7)2 · 8H2O
9.3.24WardsmithiteCa5Mg[B4O7]6 · 30H2O
9.3.27VeatchiteSr2B11O16(OH)5 · H2O
9.3.28Veatchite-ASr2B11O16(OH)5 · H2O
9.3.29 P-Veatchite
9.3.30 BalavinskiteSr2B6O11 · 4H2O
9.3.31TunelliteSrB6O9(OH)2 · 3H2O
9.3.32StrontioginoriteCaSrB14O20(OH)6 · 5H2O

Other Names for Ulexite

Other Information

Yellow, greenish yellow, cream, white.
Other Information:
Slightly decomposed in cold water and more so in hot water, with the loss of Na to the solution.
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Ulexite

Reference List:
Hayes (1844) American Journal of Science: 46: 377 (as Hydrous borate of lime).

Hayes (1844) American Journal of Science: 47: 215.

Hausmann, J.F.L. (1847) Handbuch der Mineralogie 3 volumes, Göttingen. Second edition, vol. 2, in two parts: 1429 (as Hydroborocalcite)

Ulex (1849) Ann. Chem. Pharm.: 70: 49 (as Boronatro-calcite).

Dana, J.D. (1850) System of Mineralogy, 3rd. Edition, New York: 217 (as Hayesine), 695.

Kletzinsky (1859) Polyt. Centr.: 1384 (as Tinkalzit).

How (1861) American Journal of Science: 32: 9 (as Cryptomorphite).

Des Cloizeaux, A. (1874) Manuel de minéralogie. 2 volumes and Atlas, Paris, volume 2, 1 Fasc., 208pp.: 10.

How (1877) Mineralogical Magazine: 1: 257.

Reynolds (1877) Philosophical Magazine and Journal of Science: 3: 284 (as Franklandite).

Buttgenbach (1900-1901) Société géologique de Belgique, Liége, Annales, 28, Mem. 99.

de Schulten (1901) Comptes rendus de l’Académie des sciences de Paris: 132: 1576.

van't Hoff (1907) Preuss. Ak. Wiss., Sitzber.: 303.

Foshag (1918) American Mineralogist: 3: 35.

Larsen, E.S. (1921) The Microscopic Determination of the Nonopaque Minerals, First edition, USGS Bulletin 679: 148.

Walker (1921) University of Toronto Stud., Geology series, no. 12: 54.

Mellor, J.W. (1924) A Comprehensive Treatise on Inorganic and Theoretical Chemistry. 16 volumes, London: 5: 94.

Hintze, Carl (1933) Handbuch der Mineralogie. Berlin and Leipzig. 6 volumes: 1, [4A]: 156.

Boky (1937) Bulletin de l'Académie des sciences de l'Union des Républiques Soviétiques Socialistes, Cl. sc. mat. nat., Ser. chim.: 871.

Godlevsky (1937) Mineralogicheskoe Obshchestvo, Leningrad, Zapiski: 66(2): 315 (Min. Abs. (1938): 7: 122).

Murdoch, Joseph (1940), The crystallography of ulexite: Am. Min.: 25: 754-762 (abstract): American Mineralogist: 25: 210-211.

Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II. John Wiley and Sons, Inc., New York, 7th edition, revised and enlarged: 345-348.

Clark, J.R. & C.L. Christ (1959), Studies of borate minerals, V: Reinvestigation of the X-ray crystallography of ulexite and probertite: American Mineralogist: 44: 712-719.

Weichel-Moore, E.J. and Potter, R.J. (1963) Fibre optical properties of ulexite. Nature: 200: 1163-1165.

Papezik, V.S. and Fong, C.C.K. (1975) Howlite and ulexite from the Carboniferous gypsum and anhydrite beds in western Newfoundland. Canadian Mineralogist: 13: 370-376.

Ghose, S., C. Wan & J.R. Clark (1978), Ulexite, NaCaB5O6(OH)6•5H2O: structure refinement, polyanion configuration, hydrogen bonding and fiber optics: American Mineralogist: 63: 160-171.

Canadian Mineralogist (1981): 19: 291.

Grew, E.S., and Anovitz, L.M. (1996) BORON: Mineralogy, Petrology and Geochemistry, second edition, as revised (2002).

Anthony, J.W., Bideaux, R.A., Bladh, K.W., and Nichols, M.C. (2003) Handbook of Mineralogy, Volume V. Borates, Carbonates, Sulfates. Mineral Data Publishing, Tucson, AZ, 813pp.: 722.

Internet Links for Ulexite

Localities for Ulexite

map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
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