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[SCG48-11] Hokkaidoite. New Polycyclic Aromatic Hydrocarbon Mineral and its Formation Mechanisms
Keywords:Polycyclic Aromatic Hydrocarbon, Organic Mineral, New Mineral, Coronene, Benzo[ghi]perylene, Hokkaidoite
Introduction
Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds with high thermal stability. In particular, coronene C24H12 (Cor) is the most thermally stable organic compound, which is produced by high-temperature thermal action on biogenic organic matter, and is evidence of high-temperature catastrophic events in geological age. As a mineral, Cor is known to occur rarely in hydrothermal mercury deposits as carpathite (Brumer1975, Echigo2007, etc.). However, its detailed molecular formation and purification processes are still unclear. In this presentation, we report a information on PAH minerals including the new mineral "hokkaidoite" and their formation.
Survey and results
At two sites in Hokkaido (Aibetsu area and Shikaribetsu area), we found the occurrence of various unsubstituted PAHs in hydrothermal silica veins. These were mainly composed of coronene (Cor) and benzo[ghi]perylene C22H12 (BPer), and were accompanied by miscellaneous PAHs with molecular weights of about 150-400. The former two compounds are both found as crystalline minerals, and these are the first examples of PAH minerals in Japan. The mineral composed of BPer is a pale yellow monoclinic crystal, which is approved as a new mineral hokkaidoite (IMA2022-104).
PAHs in Aibetsu occurred in hydrothermal mercury deposits (cinnabar-quartz veins). Crystals of carpathite and hokkaidoite were found in the cavities of the quartz, and other PAHs (molecular weight: 150-300) disseminated in quartz masses. Carpathite always contains a small amount of BPer as solid solution, which contrasts with the occurrence of high-purity Cor from San-Benito, CA (Brumer1975). Organic matter in Aibetsu is mainly Cor and little BPer. In Shikaribetsu, hydrothermal veins of opal A-opal CT were found in the siliceous sinter derived from paleosprings, some of which were terrestrial geyserite. This opal contained hokkaidoite, Cor crystals with a significant amount of BPer as solid solution (carpathite) , and amorphous bitumen, which is a mixture of various PAHs (molecular weight 150-400). Organic matter in Shikaribetsu was predominantly BPer.
Discussions
These organic minerals are thought to be produced from biogenic organic matter in sedimentary rocks that undergoes strong thermal and/or hydrothermal alteration, resulting in PAHs that are extracted by hydrothermal water, transported upward to near the surface, and crystallized. Also, it was found that crystallization differentiation of organic matter occurred. This crystallization differentiation has a strong tendency to crystallize in order from components that are concentration in the hydrothermal composition, have higher molecular weights, have higher molecular symmetry.
From these results, it was clarified that the formation of PAH-based organic minerals consists of three processes: (1) thermal and/or hydrothermal alteration of bioorganic matter, (2) dissolution and transportation of PAHs in hydrothermal hot water, and (3) crystallization differentiation. Also, the Cor molecule could be produced from the bottom-up process of BPer molecule with two carbon atoms, which agrees with the results of theoretical calculations (Costa 2021).
*This survey was conducted based on permission from the Ministry of the Environment.
Citation
M. Blumer, Chem. Geol., 16, 245 (1975).
T. Echigo et al., Am. Mineral., 92, 1262 (2007) .
J. C. S. Costa et al., J. Phys. Chem. A, 125, 3696 (2021).
Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds with high thermal stability. In particular, coronene C24H12 (Cor) is the most thermally stable organic compound, which is produced by high-temperature thermal action on biogenic organic matter, and is evidence of high-temperature catastrophic events in geological age. As a mineral, Cor is known to occur rarely in hydrothermal mercury deposits as carpathite (Brumer1975, Echigo2007, etc.). However, its detailed molecular formation and purification processes are still unclear. In this presentation, we report a information on PAH minerals including the new mineral "hokkaidoite" and their formation.
Survey and results
At two sites in Hokkaido (Aibetsu area and Shikaribetsu area), we found the occurrence of various unsubstituted PAHs in hydrothermal silica veins. These were mainly composed of coronene (Cor) and benzo[ghi]perylene C22H12 (BPer), and were accompanied by miscellaneous PAHs with molecular weights of about 150-400. The former two compounds are both found as crystalline minerals, and these are the first examples of PAH minerals in Japan. The mineral composed of BPer is a pale yellow monoclinic crystal, which is approved as a new mineral hokkaidoite (IMA2022-104).
PAHs in Aibetsu occurred in hydrothermal mercury deposits (cinnabar-quartz veins). Crystals of carpathite and hokkaidoite were found in the cavities of the quartz, and other PAHs (molecular weight: 150-300) disseminated in quartz masses. Carpathite always contains a small amount of BPer as solid solution, which contrasts with the occurrence of high-purity Cor from San-Benito, CA (Brumer1975). Organic matter in Aibetsu is mainly Cor and little BPer. In Shikaribetsu, hydrothermal veins of opal A-opal CT were found in the siliceous sinter derived from paleosprings, some of which were terrestrial geyserite. This opal contained hokkaidoite, Cor crystals with a significant amount of BPer as solid solution (carpathite) , and amorphous bitumen, which is a mixture of various PAHs (molecular weight 150-400). Organic matter in Shikaribetsu was predominantly BPer.
Discussions
These organic minerals are thought to be produced from biogenic organic matter in sedimentary rocks that undergoes strong thermal and/or hydrothermal alteration, resulting in PAHs that are extracted by hydrothermal water, transported upward to near the surface, and crystallized. Also, it was found that crystallization differentiation of organic matter occurred. This crystallization differentiation has a strong tendency to crystallize in order from components that are concentration in the hydrothermal composition, have higher molecular weights, have higher molecular symmetry.
From these results, it was clarified that the formation of PAH-based organic minerals consists of three processes: (1) thermal and/or hydrothermal alteration of bioorganic matter, (2) dissolution and transportation of PAHs in hydrothermal hot water, and (3) crystallization differentiation. Also, the Cor molecule could be produced from the bottom-up process of BPer molecule with two carbon atoms, which agrees with the results of theoretical calculations (Costa 2021).
*This survey was conducted based on permission from the Ministry of the Environment.
Citation
M. Blumer, Chem. Geol., 16, 245 (1975).
T. Echigo et al., Am. Mineral., 92, 1262 (2007) .
J. C. S. Costa et al., J. Phys. Chem. A, 125, 3696 (2021).