A poorly defined material, possibly a decomposition product of hornblende consisting of mica and alkali pyroxene.
A poorly defined material, possibly a decomposition product of hornblende consisting of mica and alkali pyroxene.
A poorly defined material, found as infillings in cavities in basic igneous rocks, possibly an altered chlorite or an iron-rich clinochlore.
An obsolete term for fine-grained muscovite or illite.
An obsolete term for fine-grained muscovite or illite.
See hydrotalcite group.
Pyrochroite, Mn(OH)2, structurally forms sheets of Mn(OH)6 octahedra and is isostructural with brucite. The structure is hexagonal closest packed. Pyrochroite occurs in low-temperature hydrothermal environments.
Cf., brucite
A property of crystals where an electric dipole moment develops in response to a temperature change. The material cannot exhibit temperature gradients, and the property diminishes over time at temperature. Only polar crystal classes exhibit this property. An analogous magnetic property, “pyromagnetism”, can also exist.
See groutite.
A pyramid with defined dimensions made from certain ceramic materials with different resistances to heat, used as indicators for time-temperature conditions in a kiln. Two or three pyrometric cones are placed in a kiln next to a ceramic material which is to be fired. During heating each cone softens at certain time-temperature conditions leading to a gradual kinking of each cone. Pyrometric cones are often called Seger cones named after the modern inventor of pyrometric cones, Hermann August Seger, a German silicate chemist.
The dioctahedral member of the talc-pyrophyllite group. The ideal composition is Al2Si4O10(OH)2. Pyrophyllite forms as a prominent 1A polytype (where A = anorthic, older literature refers to this polytype as 1Tc) and a less prominent, poorly crystalline 2M polytype. The stacking of 2:1 layers in pyrophyllite (Lee and Guggenheim, 1981) is not constrained by an interlayer cation as in the micas, but is related to Si4+ to Si4+ repulsions across the vacant interlayer region. Thus Si tetrahedra between adjacent layers are shifted by ~a/3 so that there are no six-fold or twelve-fold interlayer sites available for interlayer cations, as in mica. Ferripyrophyllite is the ferric iron analogue of pyrophyllite. Pyrophyllite occurs in highly Al-rich metapelites, including metabauxites and metaquartzites, and under hydrothermal conditions.
Cf., talc