The 14 Å phase developed in heated dickites

Abstract--Nacrite and dickite are found in two localities in northern Taiwan. One, containing nacrite and dickite, is associated with a gold-enargite deposit as a vug-filling clay in the Chinknshih (CKS) mine district near the northern coast. The other is the occurrence of dickite in the interstices of a Miocene coarse-grained quartzose sandstone in the Nanshihchiao (NSC) area, near Taipei city. X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscope (SEM), and petrographic examinations were used to characterize the mineralogical features. Nacrite most often takes the unusual form of rhombic platelets, and dickite is commonly elongated in habit with the shapes possibly related to their origin. Based on geological evidence, we believe that both nacrite and dickite are of hydrothermal origin. In the CKS area, the formation of nacrite and dickite is related to the hypogene gold-enargite mineralization. In contrast, the transformation of dickite in the NSC area is due to the influence of the raised temperatures of sandstone formation, resulting from volcanic activity during the Kungkuan stage after the deposition of the sandstone.

Section: Chen Wang and Yangmentioning

confidence: 99%

Mineralogy of Dickite and Nacrite From Northern Taiwan

Chen

Wang

Yang

2001

“…It should be noted that the majority of studies have concentrated on the dehydroxylation of kaolinite. Dickite has received little attention (Roy and Brindley 1956;Brindley and Porter 1978;Brindley and Wan 1978;) and hence no definitive mechanism for the dehydroxylation of dickite has been forthcoming. Differential thermal analysis results would suggest that the dehydroxylation of dickite is different to that of kaolinite (Holdridge and Vaughan 1957).…”

Section: Oh ~-~ H + + 02-and H + +Oh-~-~ H20mentioning

confidence: 99%

The Dehydroxylation of the Kaolinite Clay Minerals using Infrared Emission Spectroscopy

Frost

1996

299

138

Abstract--The dehydroxylation of a series of the kaolinite clay minerals, kaolinite, halloysite and dickite, has been investigated by Fourier transform in situ infrared emission spectroscopy over a temperature range of 100 to 800 ~ at both 50 and 5 ~ intervals. Excellent correspondence was obtained between the high temperature emission spectra and FTIR absorption spectra of the quenched clay mineral phases. The major advantage of the technique lies in the ability to obtain vibrational spectroscopic information in situ at the elevated temperature. Dehydroxylation at a number of temperatures was determined by the loss of intensity of hydroxyl bands as indicated by intensity changes of the 3550 cm ~ to 3750 cm 1 emission spectra. As with all clay minerals, kaolinite clay mineral dehydroxylation is structure dependent. No clay phase changes occur until after dehydroxylation takes place. The kaolinite clay mineral loses the inner sheet and inner hydroxyl groups simultaneously, whereas dickite and halloysites are shown to lose the outer hydroxyls, as evidenced by the intensity loss of the -3684 cm 1 peak, before the inner hydroxyl groups as determined by the intensity loss of the 3620 cm 1 peak. Evidence for a high temperature stable hydroxyl band at 3730 cm ~ for dickite and halloysite was obtained. This band is attributed to the formation of a silanol group formed during the dehydroxylation process. It is proposed that the dehydroxylation process for kaolinite takes place homogenously and involves 2 mechanisms. The dehydroxylation of dickite and halloysite takes place in steps, with the first hydroxyl loss taking place homogenously and the second inhomogenously.

“…Hill (1955) has reported the development of a 14/~-phase dickite on dehydroxylation. Brindley and Wan (1978) found that structurally well-ordered dickites give maximum development of a 14 ]k phase on heating, but that less well-ordered dickites show little or no development of this phase. The 14/k phase appeared for our dickite sample at 550~ and remained up to 800~…”

Section: Mineralogy Of Clays In the H-type Alteration Aureolementioning

confidence: 99%

Mineralogy and Genesis of Clays in Postmagmatic Alteration Zones, Makurazaki Volcanic Area, Kagoshima Prefecture, Japan

Kawano

1991

Abstract--Two distinct zonal sequences of clay minerals (H-and L-type) were found around silicified rocks in the Makurazaki volcanic area, Kagoshima Prefecture, Japan. The clay mineral sequences from the inner to the outer parts of the alteration aureoles are: 1. H-type, pyrophyllite ~ dickite ~ 2M2 mica sudoite ~ tosudite; and 2. L-type, kaolinite ~ rectorite ~ smectite. The structural formula for the sudoite is: (Al~.o4Mg,.zsFeZ+o.20Tio.03Lio.o, Ko~o2Nao.o~)(OH)rAlz.oo(Si3.s4Alo.a6)O to(OH)2. It is characterized by relatively large amounts of Mg and very small amounts of Li. The polytype is identified as IIb. The chemical analysis of tosudite shows that the sample is composed of an interstratification of sudoite-like and beidellite-like layers. The structural formula for rectorite is: (Ko.45Nao.~gCao.olMgo.00(A1Ls~Fe3+o.04-Mgo.~3Tio.03XSi3.4~mlo.59)O~o(OH)2, suggesting that the nonexpandable and expandable layers have K-micalike and beidellite-like compositions, respectively. These clay minerals in the H-and L-type alteration aureoles were formed under relatively high-and low-temperature conditions, respectively, with pH value and K-and Mg-activities increasing as the fluids ascended through the wall rocks.