BLUE COLOR IS EVERLASTINGLY APPOINTED BY THE DEITY TO BE A SOURCE OF DELIGHT

Title from John Ruskin 

Ask the average Joe or Joette on the street what comes to their mind when thinking about the color blue. Probably the first thing that pops up is something about the color of a beautiful sky (something that has been rare this winter here in the Wisconsin woods). Others may talk about the blue ocean (again not always the case) and the interviewer might wonder if they really know that water absorbs colors, like a filter, in the red spectrum of light more efficiently than in the blue spectrum? But things are quite black in ocean depths greater than about 600 feet—not much light penetration. So, does this mean that the ocean is not really blue? What it means is that our eyes see the color blue when rather clear, low-nutrient, low sediment load, water is scattered by sunlight.

More “happy” philosophical Joes and Joettes might think that blue is a relaxing color and indicates stability and serenity and wisdom while those “down in the dumps” might associate the color with the noun blues meaning a less that happy, sadder, emotion. Now an artistic sort of hipster would define blues as a musical genre, something with a “blues scale” containing twelve bars and three cords in a particular order. Think B.B. King or John Belushi and Dan Alkaroad.

Now, ask an ole rockhound like me about what comes to mind with “blue”  and out pops azurite. You know, the copper carbonate mineral that seems to define a color to those of us in the know—a soft, deep blue we refer to as azure-blue. Every rockhound in the world can picture and define azure-blue—a perfect color associated with copper minerals like azurite, or water contaminated with dissolved copper minerals leaving copper sulfate (Cu²⁺ ).  

 

A specimen of azure-blue azurite om matrix from the "Bisbee Mine" in Arizona. Width FOV ~18 mm.

Somewhere a factoid once popped into my mind that said the copper-iron sulfide chalcopyrite was the most common copper mineral. Well, azurite is the most common copper mineral that the average Joe/Joette can identify. In a beginning mineralogy class azurite, with a chemical formula of Cu₃(CO₃)₂(OH)₂, is used to study positive cations combing with negative anions to create a mineral. The divalent copper II cation combines with a carbonate anion and a hydroxide anion, and voila, out pops the beautiful azure-blue azurite.

Azurite, with its magnificent blue color has been known to the world for centuries. For example, around 2500 BCE Egyptians used the mineral in painting projects. In the early years of the AD, Pliny the Elder, a Roman jack-of-all trades, wrote the thirty-seven volume, encyclopedic Naturalis Historia and described what we now know as azurite: a deep blue mineral associated with copper deposits and used as a pigment. Today azurite is still used as an artistic painting pigment and is one of the most collectable minerals, especially in the southwestern U.S. where passing tourists seem to associate the color with the local Native Americans. Other rockhounds like me just collect it for its beauty and color.

So, we all know about blue azurite but what about other, less common, blue minerals. Well, first of all, check out the December 2020 issue of the Pick & Pack https://www.csms1936.com/wp-content/uploads/2021/02/12Dec2020.pdf ) or a revised Blog version on October 24, 2024. But now I want to introduce you to: lemanskitte, lavendulan, and gibbsite.

Gibbsite, an aluminum hydroxide [Al(OH)₃], is one of the major components of the aluminum ore, bauxite—more on that later. Gibbsite has an interesting, seemingly simple, crystal structure with stacked sheets of linked octahedra. Each of the octahedrons has an aluminum ion bonded to six hydroxide groups (hydroxide equals one oxygen atom covalently bonded to one hydrogen atom). The stacked octahedrons are weakly bonded, and the mineral has perfect cleavage (001) similar to the micas; however, rockhounds rarely observe the cleavage due to the fine size of the gibbsite particles (mindat.org). Gibbsite is a mineral of many colors from white to green to yellow to shades of blue and purple. It usually is very soft and earthy (clay-like) with only rare crystals observable. Masses of gibbsite often form spherical or clumpy aggregates that are difficult to break apart and seem easily confused in hand specimens with masses of clay minerals.

Earthy and nodular cluster of gibbsite, most of which is colored blue by "mineral mixtures" according to MinDat. Width FOV ~1 cm.

Most gibbsite is produced by the weathering of aluminum-rich minerals (perhaps micas, feldspars, corundum and nepheline) and therefore is commonly found in weathering profiles that form in tropical and subtropical environments. Here “water” leaches out soluble materials such as silica and leaves behind iron and aluminum-rich oxides. The common sedimentary rock formed in these weathering profiles is bauxite, the major ore of aluminum., composed of gibbsite, Böhmite [AlO(OH)], and its dimorph diaspore [AlO)OH)]. Mix the three minerals together with copious amounts of the clay mineral kaolinite and the “mixed up mess” is called bauxite and it is terribly difficult to identify individual minerals in hand specimens.  

Gibbsite can also form in lateritic environments without combining with other bauxite-forming minerals, sort of a “stand alone” mineral. In deeply weathered igneous and metamorphic rocks, especially granite, gibbsite can form from the weathering of feldspars and micas. However, most gibbsites are formed in areas of high rainfall and warm temperatures where aluminum-rich rocks are located.

My specimen, ~11 x 20 mm, is from the Wenshan area of China and is part of a recent discovery, ca 2012 of attractive display specimens. Composed of aggregates of botryoidal sky blue to aquamarine colors. Mineral dealers believe the Wenshan deposits may be the best intensely colored gibbsite in the world.

Lavendulan and lemanskitte are what my mother from rural Kansas would term Kissin’ Cousins, something that is of a very similar character to another thing of the same type (Oxford Languages).

Lemanskiite is a “blue” mineral, mostly with a dark sky blue color and streak, occurring as groups or aggregates of  thin tetragonal plates or prismatic, needle-like crystals, on some type of matrix, although more massive material is found filling fractures. It is a soft mineral, ~2-3 (Mohs), and has a vitreous luster. The type locality is a sulfide-rich, epithermal deposit in the famous El Guanaco Mining District, Chile. Lemanskiite is a hydrous copper, calcium, and sodium chloroarsenate: NaCaCu₅(AsO₄)₄Cl · 3H₂O.

A 6 mm cluster of rare, beautiful, blue crystals of lemanskiite collected from the Type Locality, Guanaco Mine, Taltal, Antofagasta Province, Antofagasta, Chile.

So, its cousin lavendulan, a Monoclinic mineral (lemanskiite is Tetragonal), is a slightly different blue color described as pale blue and/or greenish blue, a pale blue streak, and also quite soft with a vitreous to waxy luster. It often occurs as thin crusts of quite tiny radiating fibers as a secondary mineral in copper-arsenate deposits (such as Gold Hill in Utah), hence a hydrous copper, calcium, and sodium chloroarsenate: NaCaCu₅(AsO₄)₄Cl · 5H₂O. The specimen below is from the obscure. poly-metallic (mostly copper), Alice Mary Mine, Kundip, Raventhorp Shire, western Australia.

Pale blue, almost massive, smear of minute lavendulan crystals
 

Sub millimeter cluster of minute lavendulan crystals.

Lavendulan has an interesting history as the mineral was named for the lavender color of the original type specimen by Johann Breithaupt in 1837 found near Annaberg in the “Ore Mountains” near the German-Czech Republic boundary (current geography).  Nearly two centuries later work by Ondruš and others (2006) and Giester and others (2007) determined Breithaupt’s original type specimen was a mixture of different minerals and unrelated to the current definition/determination of lavendulan. Therefore, the second located specimen of lavendulan was found near  Jachymov, also in the “Ore Mountains” of the Czech Republic and the Type Locality was moved to that location from Annaberg.

If that is not confusing enough, lemanskiite was originally described as a polymorph of lavendulan—sharing the same mineral formula but having different internal crystal structures, in this case Tetragonal and Monoclinic Systems. But along came Zubrovka and others in 2018 and determined that chloroarsenate lemanskiite had only three “waters” in its chemical makeup in contrast with five “waters” in lavendulan. (Bet you missed that in reading the above chemical compositions!!!Check it out.

Three waters or five waters or more, many blue minerals are very difficult to identify in micromounts. I found that it is best to look at the localities as noted in MinDat and identify blue minerals from their list and go from there. For example, lavendulan and lemanskiite, those pesky “how many waters” minerals, don’t often occur together and lavendulan is a much more common mineral, especially in copper arsenic mines.

The theme of the upcoming Tucson event is Red, White, and Blue; therefore, I expect to see some quite magnificent blue specimens.   

REFERENCES CITED

Giester, G., U. Kolitsch, P. Leverett, P. Turner, P. Williams, 2007, The crystal structures of lavendulan, sampleite, and a new polymorph of sampleite: European Journal of Mineralogy, Vol. 19. No.1,

Ondruš, P., D., Veselovský, F., Skála, R., Sejkora, J., Pažout, R., Fryda, J., Gabašová, A., Vajdak, J., 2006, Lemanskiite, NaCaCu₅(AsO₄)₄Cl·5H₂O, a new mineral species from the Abundancia mine, Chile: The Canadian Mineralogist, Vol.44, No. 2.

Zubkova, N. V., Pekov, I. V., Chukanov, N. V., Kasatkin, A. V., Ksenofontov, D. A., Yapaskurt, V. O., Britvin, S. N., Pushcharovsky, D. Yu, 2018, Redefinition of lemanskiite: new mineralogicald data, crystal structure, and revised formula NaCaCu₅(AsO₄)₄Cl · 3H₂O: Geology of Ore Deposits, Vol. 60, No. 7.