In this case, a warning--that there is a lattice/formula match (12) for the two structures and that the metric symmetry exceeds crystal symmetry
for the second structure--would have been helpful.
The Photo-Atlas can be searched in various ways: by mineral name, locality, Strunz classification, physical properties (color, luster, hardness, density, streak, crystal symmetry
), chemistry and various combinations of those factors.
Have certain crystals inadvertently and unknowingly been assigned an erroneous higher crystal symmetry
? Alternatively, if a crystal is indexed on the basis of a lower symmetry lattice, is this a valid assumption?
In these chapters we read of the relations between the rhombohedral and orthorhombic carbonates and between calcite and its orthorhombic polymorph, aragonite; of calcite crystal symmetry
, and the concepts of axes, planes and centers of symmetry, and basic crystallographic forms; of pseudomorphism, and pseudomorphing of other species by and after calcite; of optical phenomena like double refraction and the polarization of light; and of fluorescence as a function of trace-element chemistry.
The crystal symmetry
can never exceed the metric symmetry, but it can be less.
, habit, cleavage, hardness, density, color, luster and transparency).
Research has shown that there exists a close link between metric and crystal symmetry
. Consequently, symmetry determination procedures based on reduction and reduced forms are widely used in the software that is associated with automated x-ray diffractometers.
and lattice parameters of two other new phases, [BaNd.sub.2][Ti.sub.3][O.sub.10], and [BaNd.sub.2][Ti.sub.5][O.sub.14], have also been identified by single crystal growth (65).
Check crystal symmetry
. Look at twinning, striations, associations, etc.
In 1784, Hauy's classic Essai d'une Theorie sur la Structure des Crystaux superseded Rome de l'Isle's Cristallographie, firmly establishing the mathematical principles underlying crystal symmetry
. Rome de l'Isle was sharply critical of the speculative nature of Hauy's theories; Hauy, in turn, chose to ignore Rome de l'Isle's work as completely as possible.