pseudocrystal

pseudocrystal

[¦sü·dō′krist·əl]
(crystallography)
A substance that appears to be crystalline but does not have a true crystalline diffraction pattern.
References in periodicals archive ?
Depending on size, this technology will eliminate the need for pseudocrystal structures for biological samples 74, 75].
And Dudley had lazurite pseudomorphs after odd things, such as a sharp, bright blue, 2-cm book-shaped pseudocrystal of lazurite replacing a mica species, embedded in white marble matrix.
Jasche (1838) mentioned specimens showing pyrolusite pseudomorphs after large calcite crystals (see under Pyrolusite), as well as gray pyrolusite pseudocrystals covered by a later generation of calcite (Jaschke, 1838).
More rarely the pocket zone produced slightly rough malachite pseudomorphs after azurite to 7 cm: Evan had five miniature to small cabinet-size specimens showing the pseudocrystals. No further specimen-bearing pocket zones have been hit since October in the Carlota mine but, Evan says, there is hope for some projected mineralized zones on the next bench down from the present workings.
The pseudocrystals, to 3.5 cm, are dull milky white but textbook-sharp, composed about equally of a tetragonal prism and a tetragonal bipyramid, with small basal pinacoid faces topping (and bottoming) off the shape.
And here's what I mean about fun facts: we are authoritatively clued in about those intriguing, earthy gray-brown pseudocrystals from Siberia which are sometimes called "achtaragdite": they are pseudomorphs of an intermediary solid solution between grossular and katoite after euhedral crystals of mayenite, an extremely rare, poorly characterized Ca-Al oxide.
And there was a flat of miniatures consisting of loose botryoidal crusts and grapy coagulations of dark to baby-blue plancheite, with malachite pseudocrystals.
The habit of the pseudocrystals varies considerably.
The pseudocrystals measure between 1 and 2 cm, exceptionally reaching 10 cm.
The malachite pseudomorphs are sharp, tabular to blocky shapes reaching 3 cm, upstanding on miniature-size matrix, the surfaces of the (completely replaced) pseudocrystals being a lush and beautiful velvety green.
Malachite shows off as rich green, botryoidal pieces with a lustrous "finish" as if highly polished; as stalactiform shapes seemingly draped in green velvet; and, of course, as big clusters of wedge-terminated pseudocrystals after azurite.