Thermal

Thermal metamorphism. Rocks formed in environments where directed stresses are not important, such as the contact aureoles around igneous bodies. Assemblages usually formed at low pressure.
  • IMG 5517 Fine dark spotting in slate - the first signs of contact metamorphism from a nearby granite. Near Godrevy Point, Cornwall.
  • IMG 5528 The distribution of spots, most likely of cordierite, relates to the aluminium content of the sediment and the bands of spots trace out original bedding. The slaty cleavage is horizontal in the photo. Near Godrevy Point, Cornwall.
  • IMG 5522 Detail of former cordierite spots in kaolinised slate, near Godrevy Point, Cornwall. The darker horizontal bands are mica-rich domains formed parallel to the tectonic cleavage.
  • IMG 5854 White andalusite crystals have formed in dark slate in a roof pendant in the Tregonning Granite, Cornwall.
  • m32-outcrop A very large thermal aureole formed beneath the mafic layered series of the Bushveld Igneous Complex, South Africa. Here, interbanded silts and shales have been transformed into andalusite-staurolite hornfels, leaving the overall sedimentary relationships undisturbed.
  • dan09 crop Andalusite porphyroblasts cover the bedding surfaces of shaly interlayers in sediments of the Pretoria Group in the aureole of the Bushveld Complex, South Africa.
  • dan05b Long andalusite prisms have grown in a homogeneous graphitic mudstone in the aureole of the Bushveld Complex, South Africa.
  • IMG 4821 Andalusite of the variety chiastolite, with the distinctive pattern of dark inclusion-rich zones inside the crystals, in the contact aureole of the Nelson batholith, SE British Columbia, Canada.
  • IMG 5828 Migmatite formed from interaction between slate hornfels and fluid-rich magma at the contact of the Tregonning Granite, Cornwall.
  • s99-14 Forsterite marble with bands and veins of yellow-green serpentine, formed from dolomitic Durness Limestone at the contact with syenite, Assynt, NW Scotland.
  • c99-01 Calc-silicate skarn composed of red-brown andradite garnet and dark amphibole, formed by fluid activity in the aureole of the Lands End granite, Cornwall.