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Encrustations from Lava Caves in Surtsey, Iceland. A Preliminary Report
... The surface encrustations on Surtsey were mainly deposited in two types of environments, as sublimates deposited directly from a gaseous state on lava and scoria at relatively high temperatures, and in a vapour-dominated system in lava craters and shallow lava caves, where steam emanation was vigorous [103]. Encrustation samples were collected in 13 expeditions from 1965 to 1998 [1]. ...
The fumarolic mineralogy of the Icelandic active volcanoes, the Tyrrhenian volcanic belt (Italy) and the Aegean active arc (Greece) is investigated, and literature data surveyed in order to define the characteristics of the European fumarolic systems. They show broad diversity of mineral associations, with Vesuvius and Vulcano being also among the world localities richest in mineral species. Volcanic systems, which show recession over a longer period, show fumarolic development from the high-temperature alkaline halide/sulphate, calcic sulphate or sulphidic parageneses, synchronous with or immediately following the eruptions, through medium-temperature ammonium minerals, metal chlorides, or fluoride associations to the late low-temperature paragenesis dominated by sulphur, gypsum, alunogen, and other hydrous sulphates. The situation can be different in the systems that are not recessing but show fluctuations in activity, illustrated by the example of Vulcano where the high-temperature association appears intermittently. A full survey of the mineral groups and species is given in respect to their importance and appearance in fumarolic associations.
... This is certainly a " golden moment " for the decoration of volcanic caves, a time when not only the ceiling, but also the walls and the floor are completely covered by an incredible variety of polychromatic stalactites, soda straws, stalagmites, flowstones, popcorn, coralloids, etc. An exceptional example of this kind of decoration was found in the Cutrona lava tube on Mt Etna (Forti et al., 1994), but other cavities around the world are known to host similar formations (Jakobsson et al., 1992;Jónsson, 1994;Davies, 1998). Unfortunately most, if not all speleothems and cave minerals deposited via this dissolution/precipitation mechanism in a still hot volcanic cave are short lived; in fact, they rapidly dissolve as the cave temperature drops and the environment becomes more humid. ...
Perhaps man’s first motivation to explore caves, beyond using them as shelter, was the search for substances that were not available elsewhere: most of them were minerals. However, for a long time it was believed that the cave environment was not very interesting from the mineralogical point of view. This was due to the fact that most cave deposits are normally composed of a single compound: calcium carbonate. Therefore, the systematic study of cave mineralogy is of only recent origin. However, although only a limited number of natural cavities have been investigated in detail, about 350 cave minerals have already been observed, some of which are new to science. The presence of such unexpected richness is a direct consequence of the variety of rocks traversed by water or other fluids before entering a cave and the sediments therein. Different cave environments allow the development of various minerogenetic mechanisms, the most important of which are double exchange reactions, evaporation, oxidation, hydration-dehydration, sublimation, deposition from aerosols and vapors, and segregation. The cave temperature and pH/Eh strictly control most of them, although some are driven by microorganisms. The cave environment, due to its long-term stability, can sometimes allow for the development of huge euhedral crystals, such as those found in the Naica caves (Mexico), but the presence of extremely small yet complex aggregates of different minerals is far more common. Future development in the field of cave mineralogy will likely be focused mainly on hydrothermal and sulfuric-acid caves and on the role played by micro-organisms in controlling some of the most important minerogenetic processes in caves.
V Savdski Arabiji je bilo raziskanih in izmerjenih več velikih vulkanskih jam v različnih poljih lave. Ena največjih je Ghar Al Hibashi na polju lave Harrat Buqum-Nawasif. To je v glavnem raven rov (400 m dolg in 15 m širok), dostopen skozi majhno brezno, ki se odpira v stranskem rovu. Jama je dolgo služila za skrivališče netopirjem, hijenam, volkovom in lisicam. Zaradi tega je dno jame, deloma iz debelih plasti nesprijetega peska, prekrito s številnimi kostmi in koproliti ter razmeroma velikimi kupi gvana. Nekateri so se bili vneli, zaradi česar so deloma zgorele tudi na njih ležeče kosti. Edine prave kapnike predstavlja nekaj majhnih, rumenih in prosojnih stalaktitov. Tekom treh odprav 2003 je bilo iz jame vzetih nekaj sekundarnih kemičnih odkladnin za mineraloške preiskave. Kljub majhnemu številu vzorcev je bilo do sedaj zaznanih vsaj 19 različnih mineralov, največ takih, ki so povezani z biogeno mineralizacijo kosti in gvana. Trije od teh, pyrocoproite, pyrophosphite in arnhemite, so izredno redke organske spojine, izključno vezane na goreči gvano. Do danes so bili ti minerali znani le iz nekaj jam v Afriki. Zahvaljujoč tem odkritjem ni jama Hibashi le najpomembnejša vulkanska jama v Savdski Arabiji, ampak tudi tamkajšnje daleč najbogatejše mineraloško nahajališče. Zato te raziskave, ki še zdaleč niso končane, potrjujejo novejše domneve, da so v jamskem okolju prav vulkanske jame najprimernejše za razvoj različnih mineralogenih mehanizmov.
Several large lava tubes have been explored and mapped in different lava fields around the Saudi Arabia. One of the largest is Ghar Al Hibashi, located in the Harrat Buqum-Nawasif lava field. It mainly consists of a huge rectilinear gallery (over 400 m long and 15 m wide) the access to which is through a small vertical pit reaching a side corridor. The cave was long used as a shelter for bats, hyenas, wolves and foxes. Therefore the entire cave floor, consisting of locally thick uncemented sand, is scattered with a great amount of bones and coprolites, while some rather large guano deposits are also found. Some of these guano deposits caught fire, which partially burnt the bones overlaying them as well. The only true speleothems consist of a few small yellow translucent stalactites. During three expeditions in 2003, a few samples of secondary chemical deposits were collected inside this lava tube to be analysed from the mineralogical point of view. Despite the scarcity of these samples, at least 19 different minerals have already been detected, most of which are related to the biogenic mineralization of bones and guano deposits. Three of them, pyrocoproite, pyrophosphite and arnhemite are extremely rare organic compounds strictly related to the guano combustion, which have been observed until now only in a few caves in Africa. Thanks to these findings Hibashi lava tube is not only the most important volcanic cave of Saudi Arabia but also by far the richest mineralogical shelter of the country. Therefore this research, which is far from coming to an end, confirms the recently advanced opinion that amongst the different cave environments, volcanic cavities are very favourable for the development of different minerogenetic mechanisms.
Après une mise en perspective historique nous présentons un rapide état des connaissances en matière de tunnels de lave et de spéléothèmes volcaniques (lavacicles). Nous jetons les bases de la contribution de la volcanospéléologie aux géosciences. Enfin, nous présentons une dizaine de tunnels de lave islandais remarquables avant de conclure sur le développement de la volcanospéléologie et l’intérêt croissant suscité par les zones volcaniques et géothermales auprès des voyageurs, spéléologues et explorateurs.
Kahf Kharrat Najem Cave is a small cave in United Arab Emirates (UAE) that hosts a bat colony which is the source of guano deposits and peculiar centimeter-long yellowish stalactites. The mineralogy and geochemistry of these deposits were analyzed using powder X-ray diffraction (XRD), energy dispersive X-ray spectroscopic microanalysis (EDX), scanning electron microscope (SEM), and stable isotope composition (δ 13 C and δ 15 N). Urea CO(NH 2) 2 was found to be the main compound of these stalactites, while allantoin C 4 H 6 N 4 O 3 was found to be an accessory urea byproduct. This paper is the first to mention allantoin in a cave environment. We also identified rare sulfate minerals (aphthitalite, alunite) and phosphates that probably correspond to the archerite-biphosphammite series. The occurrence of these rare bat-related minerals is due to the extremely dry conditions in the cave, which accounts for the extraordinary preservation of the guano deposits and allows for the crystallization of these very soluble minerals.
Natural hydrous silicas may be subdivided into three well‐defined structural groups—opal‐C (well‐ordered α‐cristobalite), opal‐CT (disordered a‐cristobalite, a‐tridymite) and opal‐A (highly disordered, near amorphous). Lussatite from the original locality is identical with opal‐CT and thus appears to be a legitimate term for this class of opal. Although the prime criterion used is the nature of the X‐ray diffraction pattern, supplementary information from infra‐red absorption, dilatometer and thermal techniques supports the three‐fold classification.
The volcanic island Surtsey, off the S coast of Iceland, was created by volcanic activity in 1963-67. Core from a 181-m-deep hole extending 123m below sea level shows the results of 12 yr of hydrothermal alteration of basaltic tephra. The primary cause of heating of the tephra and of development of the hydrothermal system was the intrusion of dikes below sea level. At present, the hottest part of the hole, at a maximum temperature of 150oC, is cooling at approx 0.9oC per year. Palagonitization of sideromelane glass, a dominant constituent of the tephra, is an important alteration process that is strongly temperature dependent, the rate doubling for every 12oC increase. Ten hydrothermal minerals have crystallized in the tephra at 25-150oC; the dominant species are smectite (nontronite), analcite, phillipsite, and tobermorite. No major differences in mineral occurrence are noted above and below sea level.-from Authors
Glossary of mineral spe-cies
- M Flcischcr
- J A Mandarino
Flcischcr, M. & Mandarino, J.A. 1991: Glossary of mineral spe-cies. Thc A4incl~alogical Record Inc., Tucsoll, 256 p