Eleven New Melanophlogite Pseudomorph Occurrences in Southern California
Last Updated: 15th Aug 2013By Robert Housley
Introduction. Since the original description of melanophlogite from the Sicilian sulfur mines (VON LASAULX, 1876) it has remained a rare and enigmatic mineral. Unaltered material is still only known from less than a dozen localities worldwide. Even from the classic localities it is frequently altered to chalcedony or quartz pseudomorphs, with little change in outward appearance, and also frequently contains included material. These characteristics complicated early efforts at analysis and characterization. (Friedel, 1890) as reported in (SKINNER and APPLEMAN, 1963). Several localities are known only from chalcedony pseudomorphs (DUNNING and COOPER, 2002).
A breakthrough in understanding the structure and paragenesis of melanophlogite occurred when (KAMB, 1965) using the x-ray powder diffraction data of Skinner and Appleman recognized that it was isostructural with one of the then known methane hydrate phases. Subsequent single crystal structure analysis (GIES and LIEBAU, 1981) confirmed this insight. Mass spectroscopic identification of the trapped gases, and subsequent successful synthesis efforts (GIES et al., 1982), at 150 bars pressure led then to suggest that it could form under ocean bottom conditions. At about 125 bars the density of atoms in an ideal gas is about equal to the density of gas atoms in the clathrate.
The suggestion of ocean bottom formation was dramatically confirmed (KOHLER et al., 1999) when a sample was dredged up from the Cascadia subduction zone off the Oregon coast.
Until recently melanophlogite was the only known silica clathrate. However, two new ones have recently been discovered in Japan bringing the total now to three (MOMMA et al., 2011).
Before melanophlogite was described a number of occurrences of chalcedony cubes were known, but were reported as “pseudomorphs after fluorite”. Since melanophlogite is rare and not widely known, this still occurs sometimes up to the present, which complicates efforts to know how widespread melanophlogite really is.
In any case it is the purpose of this note to report eleven new occurrences in Southern California. The coordinates and key characteristics of these deposits are listed in Table 1. All but one are in the Santa Monica Mountains. More detailed accounts of each occurrence then follow. Five occurrence in Northern California were earlier described (DUNNING and COOPER, 2002).
Encino. In 1936 Murdoch (MURDOCH, 1936) described what he thought were chalcedony pseudomorphs after fluorite from 5 locations in Encino, and one 4 miles east near the head of Higgins Canyon. However, he only identified the locations with the letters A through F without any more detailed position information. He identified the host rocks as sediments of the Topanga or Modello Formations. Murdoch also gives some references to earlier reported occurrences of chalcedony after fluorite. A later listing of mineral localities in Los Angeles County, (SHARP, 1959) mentions chalcedony after fluorite, as occurring near the end of Harclare Lane in Encino. The Los Angeles County Museum of Natural History has on display a sample donated in 1965 by Virgil Ketner and listed as coming from Oldham Street in Encino. It appears to be about 12 mm on an edge and might be evidence of the biggest melanophlogite crystal known. Harclare Lane and Oldham Street are close together and probably roughly define the area where Murdoch’s Encino localities were. The area is built up now so no possibility exists to study the material in place any longer.
Higgins Canyon. The location near the head of Higgins Canyon above Beverly Hills was mentioned again (NEUERBURG, 1951), but it also is totally developed and offers no chance for study now.
Lewis Road. This locality in Agoura was probably discovered in the late 1980s or early 1990s by Fred DeVito and Bill Rader. I first went there in January of 1995. The locality is accessible and easy to reach by following a graded dirt extension of Lewis Road past a gate to a water reservoir, and the following the ridge west for a short distance. The pseudomorphs occur in narrow chalcedony seams in an andesitic breccia unit of the Conejo Volcanics. Many flats of material have been collected here. An outcrop near the brush line north of the ridge has been most productive and still shows pseudomorphs in place. Also just north of a high point on the ridge is a wider vein of marcasite agate in very hard rock. Several samples from here checked by Raman spectroscopy have all proven to be pseudomorphs.
Lost Hills Road. This area, near Calabasas, was an old landslide in the Upper Topanga Formation that was excavated and repacked in about 1995. It contained a number of large septaria nodules, rarely less than two feet in diameter. Most contained little besides calcite, pyrite, and gypsum, but a few contained mostly silica minerals in a variety of odd forms. Only a small amount of cubic silica pseudomorph material was saved. The area is completely developed and totally inaccessible now.
Mountain View. In this area also near Calabasas, pseudomorphs were found by Bill Rader in a single rock, probably from the Modello Formation, exposed along Mountain View Drive just north of its intersection with Mureau Road during construction. This area is now developed as a gated community, so nothing can be seen there now.
Teal Terrace. Pseudomorphs were found by Bill Rader in a single rock, probably from the Monterey Formation, behind Teal Terrace, near Point Dume, during construction. Nothing can be seen there now.
Ladyface 1. I first visited this area on Ladyface Mountain off of Kanan Road, which is composed largely of andesites and basalts of the Conejo Volcanics, with Jason Badgley in 2005. The most direct route there would leave Kanan Road south on a ridge above a graded area just before the first big turn to the right. This is also just before a cut exposing sand and alluvial rocks on the right hand side. The melanophlogite is found in an area at the base of the lower of two big red scoria outcrops that can be seen from a distance. This is about one half mile up in the draw to the left of the ridge. There is what appears to be a basalt dike running vertically along the left side of the scoria. The melanophlogite is found in narrow chalcedony seams in both the basalt and in the red scoria. There is also calcite in the area. More material could be found here, but it will require hard rock breaking.
Ladyface 2. This is a small pit on a grassy slope, sampling a vein in an andesite breccia of the Conejo Volcanics, where Jason was collecting plume and marcasite agate and angel wing chalcedony. The melanophlogite pseudomorphs occur on the chalcedony including some of the angel wing. They are small and a few checked by Raman spectroscopy have been completely altered to chalcedony. Probably more material could be dug up here. This area is just south of a large outcrop on the ridge that shows volcanic bombs in welded tuff.
Ladyface 3. In the Spring of 2009 I parked at the first road on the right after coming over the first hill on Kanan Road, south of the 101 Freeway. I walked over a little crest in the road and down the canyon to a fork. I took the right fork and started up the west bank of a ridge, a route I had taken several times before. After passing upward through a short section of Monterey Formation shale, just as I was getting back up into the Conejo Volcanics I noticed that the rock was highly altered and contained much fine grained calcite. Although I had passed here before, this time I dug around a little and when I came to the some chalcedony I noticed sparkly crystals and took a few samples home to check. These all turned out to be nice melanophlogite pseudomorphs. I checked several using Raman spectroscopy. More material could easily be found here.
Lobo Canyon. This area is off of Lobo Canyon Road, and on a brushy slope across the creek, and near some new residential development is also in the Conejo Volcanics. The melanophlogite pseudomorphs are in loose rocks exposed by a small drainage across a gently sloping area. Several checked by Raman spectroscopy have all proven to be pseudomorphs. The crystals are small and are sparsely distributed in narrow seams. I collected some micro zeolites in situ not too far above the area, and Jason found a big quartz geode.
Reef Point. I first collected at Reef Point Drive in Newport Beach in the Spring of 2003. I learned about Even Anderson’s “melanophlogite” find there through Fen Cooper who put me in touch with Evan. I then visited Evan and confirmed the identity and significance of his material and learned the exact location
where he had found it. I made 2 or 3 trips to the area. I think on the first trip I only found one piece of chalcedony with the pseudomorphs on the graded section of Reef Point Drive where Evan said it should be. On a second trip I looked along a several block long section of graded hillside north of Reef Point Drive and found about a dozen more pieces with melanophlogite pseudomorphs. Typical examples are shown below.
On these trips I did not see any of the sedimentary rock in place. Evan has written this area up in Mineral News (ANDERSON, 2003). He identifies the host rocks as belonging to the Monterey Formation. In the article he mentions one sample he believes to be unaltered melanophlogite, but that has not yet been confirmed. Although the known collecting spots here are built up and inaccessible, is seems likely that other spots might be found nearby.
Discussion. At first glance it may seem very odd that melanophlogite would be fairly concentrated in this limited geographic area, even though it occurs in a wide variety of rock types. There is however one unifying feature. The Conejo Volcanics, which occur throughout the area, were all erupted onto, or intruded into a thick sequence of marine sediments (DIBBLEE and EHRENSPECK, 1993), (FRITSCHE et al., 1993). Bitumen is widespread in the veins of secondary minerals throughout both the volcanics and the sedimentary rocks. In fact there are active hydrocarbon seeps out of the volcanics in several places.
Acknowledgements. I especially want to thank the people, Bill Rader, Jason Badgely, and Evan Anderson, who have spent the time and effort to show me localities that I was otherwise unaware of. I also want to thank Alyssa Morgan for providing the information concerning the sample in the LA County museum. For the Raman spectroscopy I am fortunate to be able to use the equipment in George Rossman’s laboratory at Caltech under his expert guidance.
References
Anderson, J. E., 2003. Melanophlogite and its Chalcedony Pseudomorphs: A New California Location and its Unique Formational Occurrence. Mineral News 19, 1-9.
Dibblee, T. W., Jr. and Ehrenspeck, H. E., 1993. Field relations of Miocene volcanic and sedimentary rocks of the western Santa Monica Mountains, California. Field Trip Guidebook - Pacific Section, Society of Economic Paleontologists and Mineralogists 72, 75-92.
Dunning, G. E. and Cooper, J. F., Jr., 2002. Pseudomorphic melanophlogites from California. The Mineralogical Record 33, 237-242.
Fritsche, A. E., Weigand, P. W., Ehrenspeck, H. E., and Harma, R. L., 1993. Field trip guide to middle Tertiary rocks in the western Santa Monica Mountains, Southern California. Field Trip Guidebook - Pacific Section, Society of Economic Paleontologists and Mineralogists 72, 125-147.
Gies, H., Gerke, H., and Liebau, F., 1982. Chemical composition and synthesis of melanophlogite, a clathrate compound of silica. Neues Jahrbuch fuer Mineralogie. Monatshefte 1982, 119-124.
Gies, H. and Liebau, F., 1981. Melanophlogite; composition, thermal behavior and structure refinement. Collected Abstracts - International Congress of Crystallography 12, C-187-188.
Kamb, B., 1965. A Clathrate Crystalline Form of Silica. Science 148, 232-4.
Kohler, S., Irmer, G., Kleeberg, R., Monecke, J., Herzig, P. M., and Schultz, B., 1999. Melanophlogite from the Cascadia accretionary prism, offshore Oregon: First occurrence in a cold seep environment. Beth 1 European Journal of Mineralogy 11, 129.
Momma, K., Ikeda, T., Nishikubo, K., Takahashi, N., Honma, C., Takada, M., Furukawa, Y., Nagase, T., and Kudoh, Y., 2011. New silica clathrate minerals that are isostructural with natural gas hydrates. Nature Communications 2.
Murdoch, J., 1936. Silica-fluorite pseudomorphs. American Mineralogist 21, 18-32.
Neuerburg, G. J., 1951. Minerals of the eastern Santa Monica Mountains, Los Angeles City. American Mineralogist 36, 156-160.
Sharp, W. E., 1959. Minerals of Los Angeles County. Self published.
Skinner, B. J. and Appleman, D. E., 1963. Melanophlogite, a cubic polymorph of silica. American Mineralogist 48, 854-867.
von Lasaulx, A., 1876. Mineralogisch-kristallographische Notizen. VII. Melanophlogit ein neues Mineral. Neues Jahrbuch fuer Mineralogie., 250-257.
A breakthrough in understanding the structure and paragenesis of melanophlogite occurred when (KAMB, 1965) using the x-ray powder diffraction data of Skinner and Appleman recognized that it was isostructural with one of the then known methane hydrate phases. Subsequent single crystal structure analysis (GIES and LIEBAU, 1981) confirmed this insight. Mass spectroscopic identification of the trapped gases, and subsequent successful synthesis efforts (GIES et al., 1982), at 150 bars pressure led then to suggest that it could form under ocean bottom conditions. At about 125 bars the density of atoms in an ideal gas is about equal to the density of gas atoms in the clathrate.
The suggestion of ocean bottom formation was dramatically confirmed (KOHLER et al., 1999) when a sample was dredged up from the Cascadia subduction zone off the Oregon coast.
Until recently melanophlogite was the only known silica clathrate. However, two new ones have recently been discovered in Japan bringing the total now to three (MOMMA et al., 2011).
Before melanophlogite was described a number of occurrences of chalcedony cubes were known, but were reported as “pseudomorphs after fluorite”. Since melanophlogite is rare and not widely known, this still occurs sometimes up to the present, which complicates efforts to know how widespread melanophlogite really is.
In any case it is the purpose of this note to report eleven new occurrences in Southern California. The coordinates and key characteristics of these deposits are listed in Table 1. All but one are in the Santa Monica Mountains. More detailed accounts of each occurrence then follow. Five occurrence in Northern California were earlier described (DUNNING and COOPER, 2002).
Table 1. Melanophlogite pseudomorph discovery and location information | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Encino. In 1936 Murdoch (MURDOCH, 1936) described what he thought were chalcedony pseudomorphs after fluorite from 5 locations in Encino, and one 4 miles east near the head of Higgins Canyon. However, he only identified the locations with the letters A through F without any more detailed position information. He identified the host rocks as sediments of the Topanga or Modello Formations. Murdoch also gives some references to earlier reported occurrences of chalcedony after fluorite. A later listing of mineral localities in Los Angeles County, (SHARP, 1959) mentions chalcedony after fluorite, as occurring near the end of Harclare Lane in Encino. The Los Angeles County Museum of Natural History has on display a sample donated in 1965 by Virgil Ketner and listed as coming from Oldham Street in Encino. It appears to be about 12 mm on an edge and might be evidence of the biggest melanophlogite crystal known. Harclare Lane and Oldham Street are close together and probably roughly define the area where Murdoch’s Encino localities were. The area is built up now so no possibility exists to study the material in place any longer.
Higgins Canyon. The location near the head of Higgins Canyon above Beverly Hills was mentioned again (NEUERBURG, 1951), but it also is totally developed and offers no chance for study now.
Lewis Road. This locality in Agoura was probably discovered in the late 1980s or early 1990s by Fred DeVito and Bill Rader. I first went there in January of 1995. The locality is accessible and easy to reach by following a graded dirt extension of Lewis Road past a gate to a water reservoir, and the following the ridge west for a short distance. The pseudomorphs occur in narrow chalcedony seams in an andesitic breccia unit of the Conejo Volcanics. Many flats of material have been collected here. An outcrop near the brush line north of the ridge has been most productive and still shows pseudomorphs in place. Also just north of a high point on the ridge is a wider vein of marcasite agate in very hard rock. Several samples from here checked by Raman spectroscopy have all proven to be pseudomorphs.
Lost Hills Road. This area, near Calabasas, was an old landslide in the Upper Topanga Formation that was excavated and repacked in about 1995. It contained a number of large septaria nodules, rarely less than two feet in diameter. Most contained little besides calcite, pyrite, and gypsum, but a few contained mostly silica minerals in a variety of odd forms. Only a small amount of cubic silica pseudomorph material was saved. The area is completely developed and totally inaccessible now.
Mountain View. In this area also near Calabasas, pseudomorphs were found by Bill Rader in a single rock, probably from the Modello Formation, exposed along Mountain View Drive just north of its intersection with Mureau Road during construction. This area is now developed as a gated community, so nothing can be seen there now.
Teal Terrace. Pseudomorphs were found by Bill Rader in a single rock, probably from the Monterey Formation, behind Teal Terrace, near Point Dume, during construction. Nothing can be seen there now.
Ladyface 1. I first visited this area on Ladyface Mountain off of Kanan Road, which is composed largely of andesites and basalts of the Conejo Volcanics, with Jason Badgley in 2005. The most direct route there would leave Kanan Road south on a ridge above a graded area just before the first big turn to the right. This is also just before a cut exposing sand and alluvial rocks on the right hand side. The melanophlogite is found in an area at the base of the lower of two big red scoria outcrops that can be seen from a distance. This is about one half mile up in the draw to the left of the ridge. There is what appears to be a basalt dike running vertically along the left side of the scoria. The melanophlogite is found in narrow chalcedony seams in both the basalt and in the red scoria. There is also calcite in the area. More material could be found here, but it will require hard rock breaking.
Ladyface 2. This is a small pit on a grassy slope, sampling a vein in an andesite breccia of the Conejo Volcanics, where Jason was collecting plume and marcasite agate and angel wing chalcedony. The melanophlogite pseudomorphs occur on the chalcedony including some of the angel wing. They are small and a few checked by Raman spectroscopy have been completely altered to chalcedony. Probably more material could be dug up here. This area is just south of a large outcrop on the ridge that shows volcanic bombs in welded tuff.
Ladyface 3. In the Spring of 2009 I parked at the first road on the right after coming over the first hill on Kanan Road, south of the 101 Freeway. I walked over a little crest in the road and down the canyon to a fork. I took the right fork and started up the west bank of a ridge, a route I had taken several times before. After passing upward through a short section of Monterey Formation shale, just as I was getting back up into the Conejo Volcanics I noticed that the rock was highly altered and contained much fine grained calcite. Although I had passed here before, this time I dug around a little and when I came to the some chalcedony I noticed sparkly crystals and took a few samples home to check. These all turned out to be nice melanophlogite pseudomorphs. I checked several using Raman spectroscopy. More material could easily be found here.
Lobo Canyon. This area is off of Lobo Canyon Road, and on a brushy slope across the creek, and near some new residential development is also in the Conejo Volcanics. The melanophlogite pseudomorphs are in loose rocks exposed by a small drainage across a gently sloping area. Several checked by Raman spectroscopy have all proven to be pseudomorphs. The crystals are small and are sparsely distributed in narrow seams. I collected some micro zeolites in situ not too far above the area, and Jason found a big quartz geode.
Reef Point. I first collected at Reef Point Drive in Newport Beach in the Spring of 2003. I learned about Even Anderson’s “melanophlogite” find there through Fen Cooper who put me in touch with Evan. I then visited Evan and confirmed the identity and significance of his material and learned the exact location
where he had found it. I made 2 or 3 trips to the area. I think on the first trip I only found one piece of chalcedony with the pseudomorphs on the graded section of Reef Point Drive where Evan said it should be. On a second trip I looked along a several block long section of graded hillside north of Reef Point Drive and found about a dozen more pieces with melanophlogite pseudomorphs. Typical examples are shown below.
On these trips I did not see any of the sedimentary rock in place. Evan has written this area up in Mineral News (ANDERSON, 2003). He identifies the host rocks as belonging to the Monterey Formation. In the article he mentions one sample he believes to be unaltered melanophlogite, but that has not yet been confirmed. Although the known collecting spots here are built up and inaccessible, is seems likely that other spots might be found nearby.
Discussion. At first glance it may seem very odd that melanophlogite would be fairly concentrated in this limited geographic area, even though it occurs in a wide variety of rock types. There is however one unifying feature. The Conejo Volcanics, which occur throughout the area, were all erupted onto, or intruded into a thick sequence of marine sediments (DIBBLEE and EHRENSPECK, 1993), (FRITSCHE et al., 1993). Bitumen is widespread in the veins of secondary minerals throughout both the volcanics and the sedimentary rocks. In fact there are active hydrocarbon seeps out of the volcanics in several places.
Acknowledgements. I especially want to thank the people, Bill Rader, Jason Badgely, and Evan Anderson, who have spent the time and effort to show me localities that I was otherwise unaware of. I also want to thank Alyssa Morgan for providing the information concerning the sample in the LA County museum. For the Raman spectroscopy I am fortunate to be able to use the equipment in George Rossman’s laboratory at Caltech under his expert guidance.
References
Anderson, J. E., 2003. Melanophlogite and its Chalcedony Pseudomorphs: A New California Location and its Unique Formational Occurrence. Mineral News 19, 1-9.
Dibblee, T. W., Jr. and Ehrenspeck, H. E., 1993. Field relations of Miocene volcanic and sedimentary rocks of the western Santa Monica Mountains, California. Field Trip Guidebook - Pacific Section, Society of Economic Paleontologists and Mineralogists 72, 75-92.
Dunning, G. E. and Cooper, J. F., Jr., 2002. Pseudomorphic melanophlogites from California. The Mineralogical Record 33, 237-242.
Fritsche, A. E., Weigand, P. W., Ehrenspeck, H. E., and Harma, R. L., 1993. Field trip guide to middle Tertiary rocks in the western Santa Monica Mountains, Southern California. Field Trip Guidebook - Pacific Section, Society of Economic Paleontologists and Mineralogists 72, 125-147.
Gies, H., Gerke, H., and Liebau, F., 1982. Chemical composition and synthesis of melanophlogite, a clathrate compound of silica. Neues Jahrbuch fuer Mineralogie. Monatshefte 1982, 119-124.
Gies, H. and Liebau, F., 1981. Melanophlogite; composition, thermal behavior and structure refinement. Collected Abstracts - International Congress of Crystallography 12, C-187-188.
Kamb, B., 1965. A Clathrate Crystalline Form of Silica. Science 148, 232-4.
Kohler, S., Irmer, G., Kleeberg, R., Monecke, J., Herzig, P. M., and Schultz, B., 1999. Melanophlogite from the Cascadia accretionary prism, offshore Oregon: First occurrence in a cold seep environment. Beth 1 European Journal of Mineralogy 11, 129.
Momma, K., Ikeda, T., Nishikubo, K., Takahashi, N., Honma, C., Takada, M., Furukawa, Y., Nagase, T., and Kudoh, Y., 2011. New silica clathrate minerals that are isostructural with natural gas hydrates. Nature Communications 2.
Murdoch, J., 1936. Silica-fluorite pseudomorphs. American Mineralogist 21, 18-32.
Neuerburg, G. J., 1951. Minerals of the eastern Santa Monica Mountains, Los Angeles City. American Mineralogist 36, 156-160.
Sharp, W. E., 1959. Minerals of Los Angeles County. Self published.
Skinner, B. J. and Appleman, D. E., 1963. Melanophlogite, a cubic polymorph of silica. American Mineralogist 48, 854-867.
von Lasaulx, A., 1876. Mineralogisch-kristallographische Notizen. VII. Melanophlogit ein neues Mineral. Neues Jahrbuch fuer Mineralogie., 250-257.
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