A BRIEF SUMMARY OF THE MINERAL OCCURENCES AND GEOLOGY OF MONTE BIANCO
(Alps Mountains: France, Italy, Switzerland)
Author: Marco Macchieraldo
Copyright 2003 by Marco Macchieraldo.
All photos by author and specimens from his personal collection unless otherwise noted.
Draft by Laurent Gautron extracted from 'Le Regne Mineral - Hors Serie V - 1999'
Reproduction of text and photos prohibited without permission of author.
Special thanks for this article go to A.C., a cristallier of Chamonix, Savoie Department, France. In the summer of 2001 he helped me find nice specimens and gave much knowledge of climbing Monte Bianco, locating, and collecting fissure specimens. Without his help this paper would not have been possible. And thanks go to D.D., of the U.S.A. for his help in fine tuning the English translation of this Article. Neither wish to be mentioned out of modesty so only initials are used.
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Monte Bianco and adjacent regions, a famous European Alpine mineral occurrence locality has yielded a variety of mineral species, including quartz and fluorite specimens which are among the finest in the world. Mineral specimens from Monte Bianco are sought after and prized by museums and collectors from around the globe.
The Alps are the largest mountain system in Europe. The towering snow-capped peaks and peaceful valleys make them one of the most spectacular sights on the European continent.
The Alps extend northward from near the Mediterranian Sea in France and form the border between France and Italy. They continue eastward through northern Italy, Switzerland, Liechtenstein, southern Germany, Austria, and Slovenia. The entire mountain system is about 1,200 km (750 miles) in length. At their widest point, between southern Germany and northern Italy, the Alps are are about 260 km (160 miles) wide. At their narrowest point, they cover about 48 km (30 miles) in the Ligurian Alps of northwestern Italy.
Monte Bianco, at 4810 meters (15,800 feet) above sea-level, is the highest mountain peak in the Alps system and is also one of the most famous geological sights in Europe, along with the Matterhorn, another famous mountain rising to 4,478 meters (14,692 feet) above sea-level forming the border between Valais, Switzerland and the Valle dAosta region of Italy.
The ruggedness and altitude of the Alpine mountain system make travel so difficult, its presence has had an impact on human cultural development. More than 2,000 years ago few people made the difficult trip through the mountains. At that time the Roman Empire had already developed a great cicilization south of the Alps, but the culture of the people north of the mountains remained largely undeveloped. About two millenia ago the Romans built roads through several Alpine passes, and as a result, communication across the mountains increased. Only then did the Northern Peoples of Europe develop more sophisticated cultures, based upon rules and law replacing force as a means of conflict resolution.
GEOGRAPHY AND TOPOGRAPHY
The geographic boundaries of Monte Bianco toward the northwest extend into the deep Chamonix Valley, department of Savoie, France; toward the southeast the mountain and surrounding features extend into two valleys near Courmayeur, Italy: Val Ferrret and Val Veny. Toward the northeast Monte Bianco reaches into the Swiss region of Martigny. The French and Swiss sides are part of the hydrographic drainage system and basin of the river Rhone. The Italian regions of Monte Bianco is in the hydrographic drainage system of the river Po.
In this massif there are numerous mountain peaks higher than 4,000 meters above sea-level:
- 4014 meters - Dente del Gigante
- 4206 meters - Grand Jorasses
- 4248 meters - Mont Blanc du Tacul
- 4306 meters - Dome di Gouter
- 4810 meters - Monte Bianco
There are many large glaciers on Monte Bianco, most of which are located on the French side of the mountain. Mer de Glace, Glacier des Bossons, Glacier du Talefre', Glacier de Leschaux, Glacier d'Argentiere, and Glacier du Tour are significant glaciers on the French side of the mountain. But there are large glaciers on the Italian slopes of Monte Bianco as well, such as Glacier of Miage, Glacier of Brenya, Glacier of Brouillard, Glacier of Estellette, Glacier of Triolet, and Glacier of Pre du Bar.
In the following photos majestic views from the Monte Bianco massif.
Most of Monte Bianco and the surrounding regions are very difficult to reach because of the rugged terrain making travel by any means strenuous, slow, and dangerous. Accordingly, it is estimated that today only 18% of this region has been systematically explored. The remaining 82% is virgin mineralogical territory, located in the heart of Europe!
Furthermore, consider the strong erosional forces at work on Monte Bianco! Every winter there are avalanches and landslides. The expansion of the mineral water as it crystallizes at 0 degrees Celsius in the cracks and crevaces fractures rock as sure as explosives, only more slowly. With the arrival of springtime warming there is snow and ice melt run-off reshaping the mountain surfaces, along with the cold induced rock fractures, new parts of the great massif are exposed.
Typically the season of mineral collecting is limited to 2 or 3 months annually, and in many years there is no collecting done at all because of inclement weather during the 8 to 12 week window of mineral collecting. Clearly, Monte Bianco is not a site for the casual Sunday afternoon mineral collector. Only those with the knowledge, skills, and experience of Alpine mountain climbing equipped with "state of the art" climbing gear, and able to dedicate weeks or months of time can afford mineral collecting expeditions on the "White Mountain". There is a group of mineral collectors who have the needed abilities to attempt higher elevation collection. They are referred to locally as "cristalliers." These tough and rugged collectors risk their lives climbing to walls of rock searching for and removing the beautiful crystal specimens of Monte Bianco. No money received can pay for their efforts and risks. Something else must motivate the cristalliers. Perhaps it is living life at the edge, the exillaration of the climb, and a passion for crystal specimens. I would not be surprised if the finest specimens are part of the cristalliers collections.
In the above photos you can see typical places where you can find alpine fissures. Here you can have an idea about difficulties and dangers to find them.
For those less adventurous than the cristalliers, at the lowest altitudes of Monte Bianco, mainly in the morenic outwashes deposited by the glaciers, it is possible to find good mineral at these locations as well. The rocks and minerals trapped at the bottom of the glaciers are less likely to produce fine crystallized specimens because of the intense erosional forces of water flow and abrasion with the underlying granite massif. There is another process which allows fine crystal specimens to be found at these same moraines. In winter rocks are split, cracked, and detached from the mountain surface. A few of these fall onto the surfaces of the many glaciers with fine crystalline specimens undamaged. These rocks, being darker in color than the surrounding ice and snow, absorb more solar infrared electomagnetic radiation and are warmed sufficiently to melt adjacent ice and become engulfed in the glacier, isolated from hydrologic or abrasional erosional forces. In due time these rocks are at the terminus of its host glacier and drop relatively gently out of the ice and are deposited in the morenic outwash materials without having been exposed to the abrasion and hydrologic erosion of the sub-glacial rock fragments.
Some fine specimens can be found at the lower elevations by these means of transport. As a general rule, the southwest regions are rich in the more uncommon to rare mineral species. In Contrast, the northeast regions yield few of the rare occurrences, but yield large and spectacular specimens of the more common minerals. Outstanding, fabulous smokey quartz and pink fluorites can be found in this area.On the Italian side of Monte Bianco there is an occurrence of argentiferous galena. It has not been found elsewhere in the region, except in this Italian locality at the " Mine of Miage", located 3,500 meters altitude. It has been closed since the 19th century, and in the time of its operation, it was mined from 3 to 4 months per year because of the inhospitable climate. The miners slept in the mine rather than the huts provided to them because of the many avalanches. Below an old black & white photo of the mine. It's possible to see the two entries of the galleries.
Approximately 300 million years ago during the Ercynic Orogenisis, a huge granitic intrusion formed the structural base of the Monte Bianco region. Geologically recently, about 70 million years ago, a new mountain building event, the Alpine Orogenesis, uplifted the older granitic intrusion, creating many cracks and fissures in the massif. This uplifting of the Alpine Orogenesis continues to this day, but at a time in the past there was an ejection of hydrothermal fluids through the fissures. With slow cooling of these fluids mineral crystals, sometimes spectacular, grew within the cracks and fissures of Monte Bianco.
The processes leading to the growth of wonderful quartz crystals within the fissures is partially understood. Nuclear Isotope dating applied to contemporaneous Orthoclase, variety: Adularia ( nearly pure KAlSi3O8 - Potassium Aluminum silicate ), suggest that the hydrothermal ejection and subsequent growth of fissure crystals occurred approximately 18.5 million years ago. Some quartz crystals called enhydros contain fluid inclusions containning the fluids ejected at the time of their growth - 18.5 million years ago. Analysis of the fluid inclusions help to determine the thermodynamic conditions, and suggest that the pressure and temperature allowing growth of the Monte Bianco quartz crystals occurred at a depth of nearly 16 kilometers and at a temperature of nearly 400 degrees Celsius. During uplift of the overlying Ercynic rock, the granite became brittle from the underlying Alpine Orogeny forces, stretching the granite. A system of cracks and fissures developed.The super-heated water and solutes was immediately injected into the fissures, cracks, and voids as they formed. The color of the quartz are a result of the combined actions of molecular substitution by cations from the granite matrix replacing silicon in the quartz crystalline lattice and the effects of radioactive elements in the surrounding granite.
The paragenisis of the fissure mineralization is relatively simple. The succession observed: epidote, quartz, adularia, fluorite, chlorite, calcite, and a series of less frequent mineralizations - hematite, galena,etc.
Some studies of the growth of Monte Bianco quartz conclude that it was a speedy process of months or years before changes in the chemical equillibria quickly stopped crystallization.
A fluid pressure of 380 Mpascal is necessary to crystalize quartz, which is near the pressure 16km subsurface. Considering the crystals are 18.5 million years old, it can be calculated that a median lifting of Monte Bianco during the Alpine Orogeny is 0.9 mm per year.
Quartz and Fluorite are the mineral soverigns, the royalty, of Monte Bianco, producing specimens of exceptional quality, prized by collectors around the world. There are, of course, many, many other mineral occurrences from Monte Bianco and the surrounding regions. Following the more detailed Quartz and Fluorite descriptions is a partial list of Monte Bianco mineral occurrences, some with notations.
QUARTZ ( SiO2 )
As a general rule, Monte Bianco quartz crystals are stocky and of a medium size, typically ranging from 3cm to 10cm. The largest crystal discovered to this date is one of 40cm in length and they usually exhibit a macromosaic structure as a result of growth of subparrallel multiple crystals. In fissures they are often found detached from the granitic matrix because of tectonic movements, often after crystallization. Some crystals occurrences exhibit recrystallization after tectonic fracture. These are of particular interest and beauty as well.
When a crystallized pocket is located, it is often relatively easy to remove and collect the quartz crystals with the use of ones' hands and a small pry bar. To find a crystallized pocket is not so easy at all. A significant impediment is the location of the crystallized fissures, typically at altitudes of 3,000 to 4,500 meters above sea-level (approximately 10,000 to 15,000 feet), and frequently on surfaces sloping from 60% to 95% inclination from horizontal toward 90 degrees vertical. Adding to the difficulty of accessing crystallized fissures is because the surrounding rock is almost always very fractured with loose chunks, making secure footing difficult and dangerous. Many cristalliers have died from rockslides and avalanches attempting to collect these crystal fissures.
Crystal morphology of Monte Bianco quartz exhibits the usual left or right crystal forms. The above figure is a diagram showing the left and right crystallization habits. Dauphine's Law crystals are relatively common at Monte Bianco. This is a crystal twinning habit observed in quartz (and some other hexagonal system minerals) in which two right handed or two left handed crystals interpenetrate after one has revolved 180 degrees about the twinning axis. Brazil twin crystallization is rare. This is a crystal twinning habit in which the two crystals are of opposite handedness, one being right and the other left,with a face of the trigonal prism of the second order as the twinning plane. Since one is not derivable from the other by any rotation, there is no twinning axis.
Japan Law twinning, an uncommon type of quartz crystallization twinning in which in which two portions are symmetrical with respect to a trigonal bipyramid of the second order, has never been observed in quartz from Monte Bianco.
Typical of the Mount Bianco locality, but very rare and researched are the Gwindel quartzes. They result from parrallel growth on matrix of biterminated crystals. But the main axis of the crystals are rotated and form a helicoidal form of crystal. This crystal habit is named "peigne" in France, "gwindel" in Switzerland, and "elicoidali" in Italy. Study suggests that this unusual form of crystallization is caused by pyroelectricity during crystal growth when positive and negative electrical charges develop simultaneously on different parts of the same crystal in response to temperature changes suitable to evoke this electrical phenomenon. In the following drawings the growth of a gwindel quartz from the closed to the open form is explained.
The size of the gwindel specimens are generally not large, and the torsion angles range from a few degrees to an exceptional specimen with a torsion angle of 66 degrees which was found on the Aiguille Croulante near the Argentiere glacier in the northeast region of Monte Bianco.
Another interesting crystal habit of quartz is called the Scepter crystal form. In the Monte Bianco region the scepters are very rare, found less frequently than the gwindel crystals. The scepter quartz is found in only a single location in the entire region, like the gwindels, near the Argentiere glacier. Most scepter crystals have a violet amethestine color. This crystal form develops when there is a secondary recrystallization on the termination of existing quartz crystals of typical form with tardive fluids rich in copper salts.
Called "a ame" by the cristalliers, another quartz crystal habit found at Monte Bianco is the Faden crystal. These are relatively common and result from the parallel growth of plate biterminated crystals without torsion angles. The fadens are similar to the gwindels, but besides having no torsion angle, the fadens always exhibit ghosts, or phantom of earlier crystallization inside the crystal. On the left a draft with a sample of them.
The quartz specimens of Monte Bianco exhibit a range of from colors the ialine, perfectly clear transparent to black, with a continuous series of all shades of smokey quartz specimens between the two end members. The brilliance is exceptional. Even the darkest of crystals have a brilliance and transparency. I consider the quartz crystal ossurrence of Monte Bianco to be of the finest quality in the world. To add an attractive color and textural contrast, many specimens have a light coating of green chlorite on some of the crystal faces creating an esthetically pleasing effect.
Crystals exhibiting color, always have the greatest intensity of coloration at the base of the crystal. This habit is the result of two phenomena: 1.) Atomic substitution of cations for silicon in the quartz crystal lattice is more likely at the base of the crystal because of its proximity to the granite matrix to which the base of the crystal is attached, and, 2.) natural radioactivity. The structural impurities present are typically a substitution of atoms of silicon (valence +4) by aluminum (valence +3) and either hydrogen (valence +1) or lithium (valence +1). These atomic substitutions are only potential color altering centers. These must be activated by high energy short wave electromagnetic radiation, from x-rays to gamma-rays. The source of the natural radioactivity is the Monte Bianco granite which has a relatively high content of uranium (approximately 0.10 to 0.25 g/kg) and thorium (approximately 0.25 to 0.40 g/kg).
The occurrence of the many shades of quartz at Monte Bianco is also related to the altitude at which the crystals are found. This is a curious pattern which is observed. Geological experiments and studies of activation of color centers by high energy radiation explains this unusual distribution of crystal colors as a function of the altitude in which they are found. It has been demonstrated experimentally that color centers are activated at temperatures less than 225 degrees Celsius. (Keep this in mind for the moment). Quartz crystals found below 2,400 meters altitude are colorless, brilliant, and transparent as glass. Above 2,400 meters to 4,000 meters in altitude the quartz crystals are a smokey color, with the intensity of coloration increasing in direct proportion to the proximity of crystal location toward an elevation of 4,000 meters. At elevations above 4,000 meters above sea level, the quartz crystals are black and called morion quartz crystals. ( I want to note that to my knowledge, none of the Monte Bianco quartz crystals are artifically irradiated to darken crystal otherwise lighter in color.).
Since the beginning of the Alpine Orogeny, Monte Bianco has been uplifting, and continues to this day. The rock, and its fissures containing quartz crystals, at the highest elevations were cooled the more deeply seated granite. Therefore, the higher altitude quartz cooled to the transitional 225 degree Celsius (mentioned above),temperature at which the coloration centers can begin to be activated. The crystals of higher altitudes have been colder longer than the crystals at lower altitudes!
Work in progress