• Journal of the Mineralogical Society of Korea
• /
• v.12 no.1
• /
• pp.11-22
• /
• 1999

Thermal behavior of dickite was studied by thermal analysis, X-ray diffraction analysis, electron microprobe analysis, and scanning electron microscopy, Dickite has an endothermic peak at about$ 650^{\circ}C$ and an exothermic one at $960^{\circ}C$ in the differential thermal analysis. The endothermic reaction is assigned to the decomposition of dickite to meta-dickite. Hydroxyl radicals are removed from dickite structure by the reaction, resulting in the weight loss about 10.5~14.5% and appearance of a 14$\AA$ phase different from other kaolin minerals. The reaction slowly proceed in the range of $200^{\circ}C$. As the completion of decomposition, aciclular mullite forms at the expense of meta-dickite plates with random crystallographic relationship. Mullites have diverse silica versus alumina ratio. The exothermic reaction without weight loss seems to be due to the formation of spinel and amorphous silica. The spinel phase shows cryptocrystalline globular morphology accompanying a little amount of silica. From spinel phase shows cryptocrystalling globular morphology accompanying a little amount of silica. From this work, it is suggested that mullite is formed from meta-dickite much lower temperature than the reported one in the previous works.

• Korean Journal of Materials Research
• /
• v.7 no.2
• /
• pp.152-156
• /
• 1997

In this paper, I meritioned ,I study on thc rnechanochernic;~l effec ts of grountl iljckite To investigate the mechanochemical effects of ground tlickite 1,y planet,~r\- mill. a structul-ill i~nalvsis of dickite prepared with different grinding time has been made 11y X-ray diffraction and ilifierenti,~l tl~i.~-ni;~i analysis. 'l'he $SiO_{4}$ hecira was unchanged bl- milling and remained ;is the local ordering unit s t t - ~ c ~ u ~ - c ~ s in the ground dickitc samples I ) v analyzing the radial distribution function. On the other hand, with an increi~se of the grinding time a decrease of coordination number and atomic distance bet\vccn aluminum and oxygen hi1c.r l~een octurreil, and Li~~antitativcl\. coniirrned them This result corresponded to the local c,hange around aliimi~iuni I>V tliftercntii~l t1ii:rm;il ani~lysis. Therefore, the mechanochemical phenomina of ground tiickite werc3 h e to the local c~l~mge around aluminum \IT. the prolonged grinding.

• Economic and Environmental Geology
• /
• v.32 no.4
• /
• pp.399-409
• /
• 1999

Mullitization of kaolinite and dickite was examined with special attention to the influence of polytypism and impurities on the phase transformation. The phase transformation sequence in dickite is identical with that in kaolinite except that cristobalite is crystallized at $50^{\circ}C$ higher temperature in dickite. Difference in phase transformation above $1000^{\circ}C$ in kaolin minerals is attributed to the different crystal structures of metadickite and metakaolinite on the effect of impurities. A part of quartz is transformaed into cristobalite. Spinel-type phase produced in disordered kaolins including illite occurs over a short range of temperatures. Primary mullite is transformed into orthorhombic mullite at higher temperature as well. These results sustain the idea that disintegration of methkaolin and the spinel-type phase supplies extra sillica and promotes the growth of mullite cristobalite.

• The Korean Journal of Ceramics
• /
• v.1 no.2
• /
• pp.106-110
• /
• 1995

A structural analysis of dickite prepared by dry grinding with different grinding time has been made by X-ray diffraction. The $SiO_4$ tetrahedra are found to remain unchanged in the ground dickite samples by analysing the radial distribution function(RDF). On the other hand, with an increase of the grinding time a change in oxygen coordination number around aluminum has been quantitatively confirmed. This variation may be attributed to the change of hydroxyl induced by the prolonged grinding.

• Economic and Environmental Geology
• /
• v.26 no.2
• /
• pp.155-166
• /
• 1993

Gold contents with major and trace elements have been determined in 67 fresh igneous and altered wall rocks in the acid-sulfate alteration zone of the Ogmaesan-Seongsan pyrophyllite deposits in the Haenam area of the south-western part of Korean peninsula. The results are as follows; (1) Li contents have a tendency to show high value in dickite and altered rocks with dickite, while As, Mo and Sb contents have tendencies to show high values in alunite vein and silicified zone. F contents are higher in the altered rocks compared to fresh rocks. (2) Gold contents are enriched in alunite vein and silicified zone of the Seongsan deposit, but depleted in dickite and altered rock with dickite. Gold contents are especially concentrated in fault or conjunction area of two faults. (3) Gold contents are higher values in the mineral assemblages of alunite-quartz-pyrite and alteration zone of the Seongsan deposit among the studied deposits. (4) Gold contents in samples of silicified zones tend to show positive correlations with Ag, As, Co, Hg, Sb and V content, but negative correlations with Y and Zr contents, while on the other gold contents of silicified tuffs tend to show positive correlations with Hg and Sb contents. Therefore it is important to survey alunite vein and silicified zone at the conjunction of faults, and to analyze pathfinder elements such as Ag, As, Hg and Sb for geological and geochemical exploration of gold in the studied deposits.

• Journal of the Mineralogical Society of Korea
• /
• v.14 no.2
• /
• pp.119-127
• /
• 2001

FTIR spectroscopic study was undertaken on dickite and pyrophyllite with Si and Al cations in the far-infrared(Far-IR) and mid-infrared (Mid-IR) regions, respectively. Attempts were made to present bonding information and make assignments on the absorption bands of dickite in the Far-IR region. Dickites contain a small proportions or kaolinite or nacrite layers. FTIR can be used as a potential tool for characterizing the presence of mixed-layer with different polytypes of the kaolin minerals. There is no clear relationship between Hinckley index and crystallinity of dickite. Although pyrophyllite shows a strong OH stretching band at 3673-3676 $cm^{-1}$ / corresponding to an inner hydroxyl group, the weak band at $3645-3648 cm^{-1}$ seems to be due to the symmetric vibration if the symmetry of the structure is not ideal, probably due to the presence of trace Fe or mixture phases of 1Tc and 2M polytypes.

• Journal of the Mineralogical Society of Korea
• /
• v.7 no.1
• /
• pp.14-24
• /
• 1994

The Sungsan clay deposits have been formed by the hydrothermal alteration of volcanic and volcanoclastic rocks of the Hwangsan Formation of Cretaceous age. Claystones are mainly composed of dickite, alunite, illitic minerals and tosudite. The mineralogical properties of clay minerals have been studied using X-ray diffraction analysis, electron microscopy, electron microprobe analysis, and infrared absorption analysis. The physicochemical condition for the clay deposits also have been studied by the activity diagrams and mineral assemblages. Dickite, the dominant mineral in clay deposits, occurs generally as massive aggregates. It shows book-structure of well-defined hexagonal plates. Chemistry of dickite agrees with its ideal formula. Peak depth ratios in infrared absorption spectra were used for discrimination between pure and mixture of kaolin minerals. Five hydrothermal alteration zones are divided according to the mineral assemblages. From center to margin, alunite, dickite, illite and albite zones are discernible. Quartz zone occurs as small lenticular form in dickite zone. The formation of dickite and illite zones are promoted by decreasing $a_{k^+}$. An increase in $a_{H_{2}SO_{4}}$ or $a_{K_{2}SO_{4}}$ is required for the formation of alunite zone. Estimated temperature of formation ranges 110-270 $^{\circ}C$

• Journal of the Mineralogical Society of Korea
• /
• v.17 no.3
• /
• pp.267-275
• /
• 2004

A hydrothermal process was used to synthesize dioctahedral smectite from dickite [$A1_2$$Si_2$$O_{5}$ $(OH)_4$], Dickite was previously activated by heating at $800^{\circ}C$ far 4 hours with $Na_2$$CO_3$. After the heat-treatment, $SiO_2$ was added for stoichiometry, The autoclaving was carried out in closed stainless steel vessel (about 1 liter) at the condition of various temperature, pressure, time etc. High quality smectite could be obtaind by heating at $290^{\circ}C$ under the pressure of 60 kgf/$\textrm{cm}^2$ for 48 hours. This experiment reveals that pH of the solution was an important factor and should be maintained at 10 to 11 for the formation of dioctahedral smectite. The synthesized smectite was identified as Na-beidellite by the treatment of ethylene glycol and Greene-Kelly test.

• Economic and Environmental Geology
• /
• v.28 no.6
• /
• pp.571-577
• /
• 1995

Several acid-sulfate clay deposits associated with silicic magmas occur in the Haenam area of the southwestern part of Korea. Geology of the studied area consists of tuffs, granitic rocks, quartz porphyry, rhyolite, andesite and sedimentary rocks. The granitic rocks and quartz porphyry intruded tuffs and sedimentary rocks. The rhyolite and tuffs around the mines have undergone hydrothermally weak or strong alteration. Gold contents with major and trace elements have been determined for a total of sixty-seven specimens of fresh igneous rocks, wall rocks and minerals such as dickite and alunite by graphite furnace atomic absorption spectrometer and inductively coupled plasma. Gold is enriched in the alunite vein and the silicified zone, but is depleted in dickites and hydrothermally altered rocks with dickite of the Seongsan deposit. Gold is especially concentrated near the faults or conjunction area of two faults. High content of gold is shown in the mineral assemblages of alunitequartz- pyrite in the alunite vein and silicic zone of the Seongsan deposit compared with that of minerals and rocks from another deposits distributed in the studied area. Gold content in tuffs and dickites with pyrite is generally low. Gold content in silicified tuff tends to show positive correlations with content of As, Hg and Sb. Variation trends of Cd, Hg and Sb are similar to those of gold content. From the result of gold content variations, gold may be transported and concentrated by mineralizing solutions ascending along the cracks like fault. Therefore, it is important to survey alunite vein and silicified zone at the conjunction of faults, and to analyze pathfinder elements such as As, Hg and Sb for geological and geochemical exploration of gold in the studied deposits.

• Proceedings of the Petrological Society of Korea Conference
• /
• 1999.06a
• /
• pp.90-93
• /
• 1999