SUMMARY. Kerolites from Goles Mountain (Yugoslavia), Wiry (Poland), Madison Co. (North Carolina), and Kremze (Czechoslovakia) are compared with talc and stevensite. Chemical analyses give a composition for kerolite near R3Si4010(OH)2.nH20 with R mainly Mg and n about 0.8-I.2. Infra-red data and dehydration-rehydration experiments suggest that the additional water is partly surface-held hydrogen-bonded molecular water, lost up to about 3oo ~ and easily recoverable, and 'water' held as surface hydroxyls, lost at temperatures up to about 65o ~ and less easily recoverable. The surface area of kerolite from North Carolina by nitrogen absorption measurements is 196 mZ/g. X-ray data show broad basal reflections, a basal spacing (after Lorentz-polarization correction) of about 9.6 J~ and a crystallite size of about five structural layers, which is consistent with the large surface area. Two-dimensional hk bands indicate a randomly stacked layer structure with b ~ 9"I 4 A and a crystallite 'diameter' of about r5o A. The basal spacing shows no expansion in water and no thermal contraction up to 50o ~ A partial and irregular swelling with ethylene glycol is obtained only after prolonged cxposure (several weeks). In both respects, kerolites differ from stevensite. Kerolites come close to talc in structure and composition but differ in having a highly random layer arrangement, a slightly enlarged basal spacing, which could be due to misfit of layers caused by random stacking, and weaker interlayer bonding.Kerolite is considered to be a useful varietal name for this talc-like mineral in agreement with the views of D'yakonov and of Maksimovic. It cannot be defined as serpentine + stevensite.THE name kerolite, suggested by Breithaupt (I823, p. 254 ) for a mineral of waxy appearance, was derived from the Greek KVpor (wax) and 2,~0o~ (stone). In English, two spellings have been commonly used, kerolite and cerolite; the former is preferred here because it appears to have priority and reflects more obviously the Greek origin of the word. The name has appeared in most of the major mineralogical texts but over the years has tended to become discredited owing to difficulties in obtaining an adequate definition and significant chemical formula; a useful survey has been given by Stoch (1974, pp. 286-8).Occurrence. Kerolite is commonly considered to be of low temperature origin; field evidence and the colloform texture support a deposition from colloidal suspension. It occurs generally in association with weathered ultramafic rocks as coatings and as veins filling cracks and often is intimately mixed with a poorly crystalline serpentine mineral. Maksimovic 0973) found that kerolite occurred at the bottom of a weathering profile in association with partially weathered and fresh rock. This description accords with our field observations, which indicate that kerolite is consistently found only where fresh or partially altered rock outcrops.Kerolite as a mineral species. Materials called kerolites are always extremely fine-grained and often ...

Uvarovite and grossular, the former comparatively rare, occur along the serpentinite-graphite schist contact in the Fengtien area, on the eastern slope of the Central Range of Taiwan. Uvarovite occurs as small emerald-green euhedral crystals on diopside-fels with dodecahedral crystal forms and many other modifications. Its refractive index is 1.782, specific gravity 3.702, and unit cell edge 11.912 Å. Chemical and probe analyses give average Cr2O3 contents of 11.60 wt. %; spectrographic analysis shows significant enrichment in Cr, Be, Co, Y, Sb, and La over grossular. Associated minerals include nephrite, diopside, tremolite asbestos, zoisite, and clinozoisite. Grossular is reddish-brown; large crystals, dodecahedral in form often modified by trapezohedrons, are associated with diopside, idocrase, and calcite. n = 1.746, SG = 3.636, and a = 11.866 Å. Structurally and chemically it is quite near the grossular end member. Grossular is considered to be formed from pneumatolysis associated with the intrusion of ultramafic rocks, whereas uvarovite is a replacement product of relict chromite in the original ultramafic rocks where migration of elements such as silicon and calcium from wall rocks are prominent.

Beidellite clays near Chang-yuan, 80 km south of Hwalien, form vein-like bodies 5-10 m wide and 20-45 m deep. Andesitic rocks have been fractured by faulting permitting hydrothermal solutions to percolate and produce an altered mineral assemblage in which beidellite is associated with a mixed-layer illite-smeetite, kaolinite, dusty pyrite, microquartz, cristobalite, calcite and dolomite, plagioclase, and gypsum. Ca-clay is common on outcrops and subsurface, where the clay is leached, Na-clay is found; some outcrops are partly kaolinized. Chemical analyses of the beidellite show that the structure is charged predominantly in the tetrahedral sheets. Exchange capacities are mainly in the range 120-140 mEq/100 g clay (ll0~ exchangeable cations are Na >~ Ca_~Mg>K. After K saturation and heating, ten samples still expand to near 17 A with ethylene glycol, but the two samples with the highest tetrahedral charge expand only to 14.6-15.0 A although their total charge is similar to the other samples.

Dickites with well-ordered crystal structures and with relatively high dehydroxylation temperatures develop a 14 A phase when heated to temperatures in the range 550-800~ The actual spacing is close to 13-7-13"8 A. Dickites with less well-ordered structures and with lower dehydration temperatures give less development of this phase or none at all. Other kaolinite group minerals do not produce a similar phase. Thermal weightchange and differential thermal analysis data show that the 14 A phase develops to a maximum as hydroxyl ions are eliminated from the diekite structure and infrared spectroscopic data are consistent with this result. AIK~ fluorescence wavelength measurements indicate that the A1 ions are in four-fold coordination in the 14 A phase. Absence of other diffraction data makes structure analysis impossible. The description 'chlorite-like' for the 14 A phase is of questionable validity.