Hornfels


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hornfels

[′hȯr‚felz]
(petrology)
A common name for a class of metamorphic rocks produced by contact metamorphism and characterized by equidimensional grains without preferred orientation.

Hornfels

 

a dense, fine-grained rock produced by the action of an instrusive body on the enclosing rocks. Hornfels differs in composition from the rocks that have been metamorphosed. Clay rocks become hornfels containing cordierite, andalusite, sillimanite, garnet, biotite, and feldspars. Basalts, basalt tuffs, and graywackes become hornfels with pyroxenes, basic plagioclase, and hornblende. Marls become hornfels with wollastonite, olivine, spinel, and carbonates. As the quantity of carbonates increases, hornfels become contact marbles.

References in periodicals archive ?
Once leaving Hobbs 1 pipe, the hole entered into a very strongly altered and skarnified zone of hornfels characterised by semi-continuous zones of intense stockwork quartz veining.
Its blank was a pebble of spotted pelitic hornfels (cordierite hornfels), which they said 'are abundant in the Nepean River gravels, coming from a bedrock source in the upper Coxs River'.
The mineralization is hosted in a wide and intense zone of biotite hornfels with abundant pyrite and arsenopyrite within Knob Hill Formation sediments (Table 1).
The majority of tools in the Booroola 3 assemblage were made on silcrete (46 percent), followed by hornfels (36 percent) and crystal quartz (18 percent).
The country rock is a hornfels which was brecciated and altered in the Schneckenstein vent pipe.
In samples from the Zbojeckie Skaly activity concentrations of this radionuclide don't differ much, but the lowest value was noted in granite (1075 [+ or -] 23 Bq x [kg.sup.-1]) whereas the medium and the highest value refers to the sample collected from the contact between granite and hornfels (1122 [+ or -] 24 Bq x [kg.sup.-1]) and to hornfels (1199 [+ or -] 26 Bq x [kg.sup.-1]) respectively.
These structures are associated with increased K-feldspar, magnetite, chlorite, silica, and carbonate alteration, and monzonite composition hornblende and plagioclase porphyry dyke/sill lithologies in Late Triassic-Early Jurassic porphyritic monzonite host-rock as well as hornfels in Inzana Formation (Takla Group) volcanic and sedimentary host-rocks.
The shear hosted gold-silver mineralization on the Weaver Property is hosted by faulted Lower Jurassic Harrison Lake Formation volcanics and volcaniclastic sediments which have hornfels overprinting from an Oiligocene to Miocene granodiorite intrusion.
Subsequently the late Variscan Logrosan granite intrusion gave rise to a contact metamorphic aureole represented by an inner hornfels zone and an outer zone of spotted phyllites and chlorite schists (Chicharro et al., 2015).
The member here consists of massive hornfels, in which the cleavage has been largely annealed, and originally finer-grained pelitic units display strongly pitted surfaces due to weathering of coarse retrogressed cordierite porphyroblasts.
Hole GHD007 is oriented toward the NE, and was designed to target the NE edge of Hobbs Pipe 1 near the surface, and continue on to test the geology beneath historical highly anomalous hornfels metasediment hosted mineralisation.
Most Stones of the region are penetrative granite, metamorphic shiest and hornfels and Fourth period alluvium.