UNFORBIDDEN GEOLOGY  
 
Feldspar, felspar, microcline (amazon stone, amazonite, green feldspar, malachite, emerald, mother of emerald)
Archae Solenhofen (solenhofen@hotmail.com)
(Last modified April 10, 2001)

   Feldspars are any members of a group of nearly 20 related aluminosilicate rock-forming minerals, which make up the largest part of the Earth's crust (about 60%). Crystals are generally blocky, or tabular in habit. The colour is variable and usually off-white, yellowish, flesh pink, brown, or green. Luster is vitreous to sometimes pearly, or dull if weathered, and crystals can be translucent to opaque. Cleavage is perfect in one and good in another direction and fracture is conchoidal. Feldspar ranges in hardness depending on its composition from 6 - 6.5 on the Mohs' scale. Microcline (potassium aluminum silicate (KAlSi3O8) is a common mineral, and has been used as a semi-precious stone under the names of amazonite and perthite. Amazonite is a variety that is deep green and is suitable for carving and polishing. The perthite variety is a stripped stone, produced from lamellar intergrowths within crystals.

    A green (sometimes bluish) coloured microcline (amazonite) may have been obtained by the ancient Egyptians from numerous possible sources in the Eastern desert of Egypt, as either eroded sediments or mined from seams in igneous rocks. It may also have been imported form localities outside of Egypt (Lucas and Harris, 1962). As well as being used as minerals, feldspars are major constituents of many rock types used by the ancient Egyptians (igneous, metamorphic and sedimentary), including granite, granodiorite, diorite, anorthosite, gabbro, diabase, dolerite, basalt, and greywacke.

   Microcline was used by the ancient Egyptians to a limited degree for beads, inlay, and small items. Microcline was used from the Neolithic period onward, but showed its most extensive use during the 12th dynasty (Lucas and Harris, 1962). Artifacts made of microcline have sometimes been misidentified as other minerals, including malachite and emerald (it is often called "mother of emerald"). Feldspar was used by the ancient Egyptians in the making of fused glass along with quartz sand, and glass paste was posibly used as imatation green feldspar.

References

Lucas, A. & Harris, J.R. (1962) Ancient Egyptian materials and industries. E. Arnold, London, 523 p.
 
 

Links to examples of feldspar usage

a) Misc objects

Middle Kingdom period (12th Dynasty) pectoral with the name of Senwosret II made of gold, carnelian, feldspar, garnet, and turquoise (lenght: 8.3 cm: Metropolitan Museum of Art, New York).