van Driel, "Second- and third-harmonic generation from cubic centrosymmetric crystals with vicinal faces
: phenomenological theory and experiment," Journal of the Optical Society of America B, vol.
The best milarite crystals seem to come from the more alkaline environments: Weiss (2004) suggests that the smooth-faced crystals from the alkaline syenite of Val Giuv formed in something close to the mineral's "ideal" conditions in a quartz-poor environment, while by contrast the milarite crystals from the South Tyrol, some of which are associated with quartz, display countless lancet-shaped vicinal faces
, reflecting uneven patterns of growth.
Often one sees more or less distinct vicinal faces
modifying the prism faces and, much less frequently, the rhombohedron faces.
Intrasectoral zoning is often evidenced by different cathodoluminescence colors on different vicinal faces
of growth hillocks.
The third length scale features are spirals found on terraces forming the vicinal faces
of the second-order hillocks.
This holds true for crystals smaller than 2 mm, whereas larger examples show fewer forms and have faces that possess typical luster but are not even because of the many vicinal faces. Such crystals are only translucent.
Vicinal faces typical for quartz crystals are frequently present.
Polygonized growth hillocks exhibit vicinal faces
which are very shallow surfaces that vary only slightly in angle from the crystal face.