Discovery of halloysite books in altered silicic Quaternary tephras, northern New Zealand

Abstract

Hydrated halloysite was discovered in books, a morphology previously associated 29 exclusively with kaolinite. From ~1.5 μm to ~1500 μm in length, the books showed 30 significantly greater mean Fe contents (Fe2O3 = 5.2 wt%) than tubes (Fe2O3 = 3.2 wt%), and 31 expanded rapidly with formamide. They occurred, along with halloysite tubes, spheroids, and 32 plates, in highly porous yet poorly-permeable, silt-dominated, Si-rich, pumiceous rhyolitic 33 tephra deposits aged ~0.93 Ma (Te Puna tephra) and ~0.27 Ma (Te Ranga tephra) at three 34 sites ~1020 m stratigraphically below the modern land-surface in the Tauranga area, 35 eastern North Island, New Zealand. The book-bearing tephras were at or near saturation, but Halloysite is a 1:1 kaolin-subgroup clay mineral with a similar composition to 49 kaolinite, but with interlayer H2O ("water") that can easily be driven off, giving hydrated and 50 dehydrated end members in a series of forms. It is this interlayer H2O (or evidence of its 51 removal) that characterises halloysite relative to kaolinite (Churchman & Carr, 1975). The 52 fully hydrated form has a 1.0 nm (10 Å) basal spacing, and the fully dehydrated form has a 53 basal spacing of 0.7 nm (7 Å). Halloysite can adopt a continuous series of hydration states, 54 from 2 to 0 molecules of H2O per Si2Al2O5(OH)4 aluminosilicate layer, and these are 55 interpreted as a type of interstratification of the two end-member types (Churchman et al., 56 1972;Churchman & Lowe, 2012;Churchman, 2015;Joussein, 2016). Under ambient 57 environmental conditions, dehydration of halloysite is an irreversible process (Churchman et 58 al., 1972;Joussein et al., 2005;Keeling, 2015). However, the effective reversal of the basal-59 spacing change associated with the dehydration of halloysite by the addition of formamide 60 provides a common test for distinguishing halloysites from kaolinite (Churchman et al., 1984, 61 2016). 62The first application of electron microscopy to a halloysite (Alexander et al., 1943) 63 showed it to have particles with fibrous/tubular shapes. Subsequently, many halloysites 64 were found to occur as tubes. However, halloysites have also been found to occur in many 65 different shaped particles. Joussein et al. (2005) Churchman (2015), these may be grouped into four main morphological types, namely 68 tubular, platy, spheroidal, and prismatic. Of these, the spheroidal form of halloysite occurs 69 with a frequency comparable to that of the tubular form (Cravero & Churchman, 2016). 70Platy forms include a range of tabular shapes such as "crumpled lamellar" and "crinkled 71 film" forms and all these invariably have a high Fe content (Bailey, 1990 Taupo Volcanic Zone (TVZ) with respect to the Tauranga study area (after Leonard et al., 2010). 122Locations of the three main study sites at Pahoia, Omokoroa, and Tauriko, and an auxiliary site at 123 (Briggs et al., 1996(Briggs et al., , 2006Leonard et al., 2010). 144 These intercalated pyroclastic, volcaniclastic, and sedimentary d...

Halloysite in Different Ceramic Products: A Review

“…We believe that, in order to investigate the effect of halloysite presence, quantitative analyses should be provided, coupled with a thorough discrimination of kaolinite group minerals using IR and the formamide testing when needed [ 59 ]. In some cases, this discrimination was based on the crystal morphology, which is not always correct [ 60 ]. The effect of halloysite-clay raw material composition and halloysite content in the formation and firing processing.…”

Global Occurrence, Geology and Characteristics of Hydrothermal-Origin Kaolin Deposits

“…The globular cluster microstructures appear to represent an original growth habit as the result of in situ crystallization from a solution phase, and these globular clusters show diameters of 80-200 nm with unrolled particles adjacent to each other (Figure 1f). Possible spherical growth of halloysite on the edges of kaolinite flakes and altered feldspar grains, developing bending crystals and curved surfaces, may have formed through the rapid dissolution and continuous distribution of crystal dislocations [34][35][36]. Pseudo-spherical or spheroidal halloysite is related to the saturation state of solutions.…”

Using Soil Stratigraphy and Tephrochronology to Understand the Origin, Age, and Classification of a Unique Late Quaternary Tephra-Derived Ultisol in Aotearoa New Zealand

“…Once a paleosol is isolated any changes may be regarded as largely diagenetic, not pedogenic, especially when cut-off completely from surface processes [44]. Diagenesis is the post-depositional, low-temperature alteration of geological deposits or (buried) soils [131], which contrasts with alteration via pedogenesis in modern (surface) soils. Diagenesis may overlap with soil welding, which has occurred in the older Hamilton and Kauroa Ash beds as described in the text.…”

“…This situation may be compared with the dissolution kinetic-fluid flow coupling model developed by Shikazono et al [159] to explain the ongoing generation and downward migration of monosilicic acid from the weathering of multiple middle-to late-Holocene basaltic tephra layers that had accumulated layer by layer in central Japan. The coupling model was also invoked to help explain abundant halloysite formation at depth in thick accumulating Quaternary-aged siliceous tephras and derivatives in eastern North Island [131]. In the coupling model, rainwater migrates downwards through a glass-dominated tephra layer (in effect a 'silica reservoir') and reacts with the volcanic glass, which dissolves through hydrolysis, the dissolution products [Si] and [Al] then crystallizing together as halloysite.…”