Meteorite Book: Glossary F
FELDSPATHOID GROUP - Minersals occuring in low-Si terrestrial rocks, feldspathoids are similar to feldspars in structure and properties, but contain about two-thirds as much silica as alkali feldspar. They do not coexist with quartz, because the excess of SiO2 converts feldspathoids into feldspar. The most common feldspathoids are: nepheline, NaAlSiO4, falsilite, KAlSiO4, and leucite, KAlSi2O6. Their compositions can be displayed using a tetrahedron with quartz at the apex (below). The ranges of observed substitutions are shown by the colored fields.

and here is the kicker : using the language of the birds:
Nephilim - Wikipedia, the free encyclopedia
Niphilim: The Nephilim (plural) are the offspring of the "sons of God" and the "daughters of men" in Genesis 6:4, or giants who inhabit Canaan in Numbers 13:33. A similar word with different vowel-sounds is used in Ezekiel 32:27 to refer to dead Philistine warriors.
Nepheline, also called nephelite (from Greek: νεφέλη, "cloud"), is a feldspathoid: a silica-undersaturated aluminosilicate, Na3KAl4Si4O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites. It is often found in mica schist and gneiss.
Nepheline crystals are rare and belong to the hexagonal system, usually having the form of a short, six-sided prism terminated by the basal plane. The unsymmetrical etched figures produced artificially on the prism faces indicate, however, that the crystals are hemimorphic and tetartohedral, the only element of symmetry being a polar hexad axis. It is found in compact, granular aggregates, and can be white, yellow, gray, green, or even reddish (in the eleolite variety). The hardness is 5.5 - 6, and the specific gravity 2.56 - 2.66. It is often translucent with a greasy luster.
The low index of refraction and the feeble double refraction in nepheline are nearly the same as in quartz; but since in nepheline the sign of the double refraction is negative, while in quartz it is positive, the two minerals are readily distinguished under the microscope
Nepheline crystals are rare and belong to the hexagonal system, usually having the form of a short, six-sided prism terminated by the basal plane. The unsymmetrical etched figures produced artificially on the prism faces indicate, however, that the crystals are hemimorphic and tetartohedral, the only element of symmetry being a polar hexad axis. It is found in compact, granular aggregates, and can be white, yellow, gray, green, or even reddish (in the eleolite variety). The hardness is 5.5 - 6, and the specific gravity 2.56 - 2.66. It is often translucent with a greasy luster.
The low index of refraction and the feeble double refraction in nepheline are nearly the same as in quartz; but since in nepheline the sign of the double refraction is negative, while in quartz it is positive, the two minerals are readily distinguished under the microscope
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