Journal of the Mineralogical Society of Korea (한국광물학회지)

The Mineralogical Society of Korea (한국광물학회)
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Microstructural Intergrowth of Margarite and Chlorite in a Schist from Unkyori formation of Miwon Area

미원지역 운교리층 편암에서 산출하는 마가라이트와 녹니석의 미세 협재조직

  • 이승준 (충북대학교 지구환경과학과) ;
  • 안중호 (충북대학교 지구환경과학과)
  • Published : 2003.09.01
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Abstract

Margarite, occurring in an Unkyori Formation of Miwon area, Chungcheongbukdo, South Korea, was investigated using a high-resolution transmission electron microscope (HRTEM) to reveal the microstructural intergrowth textures of margarite. HRTEM images of margarite, which was previously confirmed to have intergrowth textures by petrographic microscope and back-scattered electron images, show that chlorite occurs as thin packets of layers interlayered within margarite crystals, and intercalated chlorite layers are intergrown irregularly in areas as a few hundred angstroms thick slabs or isolated chlorite unit layers. Margarite crystals observed by HRTEM consist of a well-ordered 2M polytype, and electron diffraction pattern shows no prominent streaking along the 001 (or $c^{*}$) direction, indicating that there is no significant stacking disorder in margarite. Intercalated extra brucite-like layers, which are approximately 5 $\AA$ thick, are observed locally within margarite crystals. Insertion of such extra brucite-like layer at the interlayer of margarite would result in a chlorite-like structure unit. (001) margarite layers are parallel to (001) of chlorite, and margarite layers are not extended from (001) of chlorite, indicating that margarite was apparently produced through a dissolution-precipitation mechanism.m.

충청북도 미원지역의 운교리층 내에 산출하는 마가라이트(margarite)를 고분해능 투과전자현미경(HRTEM)을 이용하여 단위포 규모의 미세한 협재조직에 관하여 조사하였다. 편광현미경과 후방산란전자 영상을 이용하여 기존에 확인된 녹니석의 협재조직을 보여주는 마가라이트 결정들을 투과전자현미경으로 관찰한 결과, 마가라이트 결정내에는 녹니석이 흔히 얇은 packet 형태로 매우 불규칙하게 협재되어 있으며, 그 두께는 수백 $\AA$에 달하거나 부분적으로 녹니석 layer가 개별 단위로 나타나기도 한다. HRTEM으로 관찰한 마가라이트는 매우 규칙적인 2M 다형구조를 보여주며, 전자회절 패턴에서 001 (또는 $c^{*}$ ) 방향으로 강한 streaking을 보여주고 있지 않기 때문에 stacking disorder가 심하지 않은 것으로 판단된다. 마가라이트 packet내에는 두께가 $5 \AA$인 부르사이트 layer들이 부분적으로 관찰되는데, 마가라이트 layer사이에 이러한 부르사이트 layer가 단위포 규모로 협재되어 부분적으로 녹니석 구조를 형성한다. 마가라이트의 (001)과 녹니석의 (001)은 서로 평행하지만 두 광물간의 구조적인 연속성이 결여되어 있으므로, 이러한 특징은 마가라이트내에 발견되는 녹니석은 용해와 침전 작용에 의해서 생성되어 협재조직을 이루었음을 지시한다.

Keywords

References

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