Dispersion biaxial crystals

The ability to dr aw approximately 100 - A diameter fibrils from PTFE dispersion particles, either by fracture after cold compaction [34] or by uniaxial or biaxial expansion of sheets or tubes after paste extrusion (extrusion of mixtures of the dispersion particles and lubricants such as mineral spirits) and lubricant removal [35], was demonstrated a number of years ago. The former process results in the development of a myriad of fibrils spanning the gap between the fracture faces these were utilized for ED characterization of the PTFE conformation and crystal packing. 

Dawsonite [Named after the Canadian geologist John William Dawson (1820-1899), principal of McGill University, Montreal, Canada] (ICSD 100140 and PDF 42-1346) NaAl(C03)(OH), M= 144.00 15.97 wt.% Na 8.34 wt.% C 18.74 wt.% Al 1.40 wt.%H 55.56 wt.%0 Orthorhombic a = 673 pm bs 1036 pm c 558 pm P.G. 2/m2/m2/m S.G. Imam (Z= 4) Barentsite type Biaxial (-) a= 1.462 P= 1.542 Y= 1-596 5=0.130 27=76.75" Dispersion weak <3 2420 (2434) Habit thin encrustations, bladed, needle-hke or radial crystals. Color colorless to white. Diaphaneity transparent. Luster vitreous to silky. Fracture uneven. Cleavage [110] Perfect. Streak colorless. Other fluorescent under short-wavelength UV with dull white. Occurrence low-temperature hydrothermal mineral. 

Figure 2. Various crystal orientations (a) random orientation, (b) one-degree orientation or fiber, (c) two-degree orientation or biaxial, and (d) single-crystal orientation. The curved double arrows indicate deviations from the preferred directions (blue and red arrows) or dispersion. From [3].

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