Columnar-jointed tuffs (bentonites) are located below the Lower Carboniferous Tideswell Dale Sill, Derbyshire, in an abandoned quarry. There are three zones of prismatic joints, columnar joints (∼60 cm thick and mean column width of 4.1 cm) and massive, conchoidally fractured rock sequentially from the dolerite contact downwards. The rocks are very fine-grained (1–10 µm) and consist mainly of sanidine, interlayered illite/smectite, and hematite, with minor quartz, apatite, montmorillonite, anatase and detrital minerals. High K2O and Fe2O3, low Na2O and low MgO are interpreted as due to alteration of felsic volcanic ash. The bentonite was contact-metamorphosed by the sill to temperatures of c. 300 °C. The progression of fracture geometries, thermal considerations and application of theories of column formation indicate that columns formed downwards away from the sill, due to prograde contact metamorphism of the originally clay-rich bentonite. The formation of columnar fracture networks by shrinkage due to igneous heating may have implications for the effectiveness of bentonite as a barrier for disposal of high-level radioactive waste. Regional dimensions include documenting widespread felsic explosive volcanism and inferring a Triassic oxidation event from palaeomagnetic data.

中文翻译：

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英国德比郡 Tideswell Dale 玄武岩基台下方的柱状节理膨润土：在前进接触变质作用过程中形成

柱状节理凝灰岩（膨润土）位于德比郡下石炭统 Tideswell Dale Sill 下方的一个废弃采石场中。从辉绿岩接触点向下依次分为棱柱节理、柱状节理（约 60 cm 厚，平均柱宽 4.1 cm）和块状贝壳状断裂岩石三个区域。岩石粒度非常细（1-10 µm），主要由山宁石、层间伊利石/蒙脱石和赤铁矿组成，少量石英、磷灰石、蒙脱石、锐钛矿和碎屑矿物。高钾2氧和铁2○3, 低钠2O 和低 MgO 被解释为由于长英质火山灰的改变。膨润土通过窗台接触变质至C. 300℃。裂缝几何形状的进展、热学考虑和柱形成理论的应用表明，由于最初富含粘土的膨润土的推进接触变质作用，柱在远离基台的地方向下形成。由火成岩加热引起的收缩形成柱状裂缝网络可能对膨润土作为高放废物处置屏障的有效性产生影响。区域维度包括记录广泛的长英质爆发性火山活动和从古地磁数据推断三叠纪氧化事件。