• Journal of the Mineralogical Society of Korea
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• v.16 no.1
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• pp.91-106
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• 2003

XRD results on annealing studies of Na-feldspars (Amelia albite) show rapid changes in the lattice parameters of the $1073^{\circ}C$-heated samples owing to disordering of Al and Si as well as lattice distortions upon quenching of the heated specimens. While a low albite transformed to a high albite by 7-days annealing at $1073^{\circ}C$, it remains as an early intermediate albite even by 140-days annealing at $924^{\circ}C$ due to the slower Al-Si disordering rate. From the heated samples tweed structures of $100∼200\AA$ were typically observed by TEM, which showed different ways of development between the $1073^{\circ}C$ -heated one and the $923 ^{\circ}C$ -heated one. The former locally trans-farmed to rnicrostructures similar to albite twin, while the latter transformed to domain structures containing albite twin plane in the wider area. The origin of tweed structures is suggested to be formation of incipient twins (albite twin and pericline twin) to reduce the lattice instability which is increased by disordering of Al and Si as well as quenching.

• Journal of the Mineralogical Society of Korea
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• v.18 no.3 s.45
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• pp.155-164
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• 2005

Volcanic rocks from the Mt. Mudeung area which are composed of Hwasun andesite, Mudeungsan dacite and Togok rhyolite contain plagioclase phenocrysts in common. Majority of the repeated twins observed in optical microscopy are albite twin and some are pericline twin. EPMA studies of plagioclases from Hwansun andesite, Mudeungsan dacite and Togok rhyolte indicate calcic andesine, andesine-oligoclase, nearly pure albite, respectively Albite twin and pericline twin can be easily distinguished through TEM diffraction patterns, which is quite difficult by optical microscopy. Plagioclases in volcanic rocks from the Mt. Mudeung area do not show e-reflection in (100) electron diffraction patterns, probably because of their high cooling rate, which inhibited phase separations during cooling.

• Journal of the Mineralogical Society of Korea
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• v.16 no.3
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• pp.233-243
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• 2003

Microstructures and chemistry of anorthoclase, a high-temperature phase of alkali feldspars, were studied using EPMA and TEM. BSE images of anorthoclase displayed mixtures of Na-rich areas and K-rich areas forming lamella of various sizes. EPMA analysis indicated that the Na-rich area is composed of Ab: 81%, Or: 3% and An: 11% in average, while the K-rich area is composed of Ab: 45%, Or: 44% and An: 11 % in average. TEM analysis revealed albite with Albite twins in the Na-rich area, contrasting to mixtures of albite with fine Albite twins and orthoclase without twins, forming regular lamella of about 100 nm sizes, in the K-rich area. The [001] electron diffraction pattern of the K-rich area also indicated coexistence of the two phases. While streaking parallel to the (010)$^{*}$ direction appeared only in albite due to the twin structure, streaking parallel to the $(100)^{ *}$ direction appeared both in albite and orthoclase, probably due to strain on the interface as well as order-disorder phenomena of Al and Si. It is suggested that the reverse orientation of albite and orthoclase is caused by pole switching to reduce strain on their interfaces. Based on these observations and analyses, the mineral studied is identified as lower-temperature cryptoperthite rather than high-temperature anorthoclase, which has a midium degree of Al-Si ordering and $400^{\circ}C$∼$600^{\circ}C$ of estimated temperatures for the microstructure formation.

• Korean Journal of Heritage: History & Science
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• v.39
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• pp.219-242
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• 2006

Quantitative analysis and provenance interpretation of the raw materials for the jade (amazonite) excavated from the Asan Sijeonri site were studied. Geology of the Sijeonri site composed mainly of Precambrian metasedimentary rocks and the alluvium ranges extensively. In the site, amazonite jade was excavated in the Bronze Age No. 4 circular-shaped resident site. The jade has a comma-shaped and shows light green color with so much cracks. The jade is silicate mineral of columnar habits that is shown white streak, and has fine cleavages with vitreous luster. As the analytical results, this jade was identified as a feldspar-group mineral gemologically called amazonite that is mineralogically microcline formed to intergrowth of albite and orthoclase. Internal textures of the amazonite present Na-end member of albite coexisting with K-end member of orthoclase that are replaced each other along the cleavages and twin planes with several ${\mu}m$ scales. Therefore, the amazonite is one mineral phase combined with albite and orthoclase by substitution of $Na_2O$ and $K_2O$, respectively. The Danyang are is an unique producing site of amazonite in South Korea, and Gongju Janggimyeon was known as microcline provenance to the utmost area from the Sijeonri site. In the marginal area of southern coast in Korean Peninsula, Bronze Age amazonite has been excavated in several sites, where original provenance of the raw amazonite is not identified. The Sijeonri site does not show any facilities of producing and processing traces for amazonite jade. Also, only one jade was collected in the Sijeonri site. Therefore, there is not possibility that the provenance of raw jade is the Sijeonri area. To explain original provenance of the amazonite jade, migration path, manufacturing process and archaeological interpretation are required.