ON U&EFUL AND ORNAMENTAL STONES OP ANCIENT EGYPT. 



" From Old Temple, Gizeh. 



" This is a medium-grained basalt (plagioclase basalt), in 

 all probability belonging to the subdivision of olivine Basalts. 



" It is composed of plagioclase, augite, olivine (?), iron 

 ore, and apatite, with a small amount of glass. 



" Under the microscope, the rock is seen to be porphyritic, 

 a few larger individuals of plagioclase and augite occurring 

 scattered through the rock. These porphyritic plagioclase 

 crystals are occasionally somewhat decomposed. The rest 

 of the plagioclase occurs in well-twintied, lath-shaped crystals, 

 and is quite fresh. The augite is often well crystallised, and 

 shows its characteristic cleavage and inclined extinction. 

 There are also a number of more or less rounded grains which 

 seem to have been olivine, but which are now almost entirely 

 altered to a brown decomposition product, showing aggre- 

 gate polarisation, and which is apparently for the most part 

 hydrated ferric oxide. This material stains the other minerals 

 of the rock, and seems in some cases to result also from the 

 decomposition of the augite or the glass. The iron ore, 

 which is black and opaque, resembles magnetite, and occurs 

 in irregular-shaped grains. The apatite is somewhat abun- 

 dant, occurring in long, slender needles." 



A rock of this kind is described by Zittel and by Beyr'ich 

 and Schweinfurth as forming eruptive masses in Lower Egypt, 

 and probably of Tertiary age. One locality is at Abu Zabel 

 less than 20 miles to the north-east of Cairo, and other 

 localities occur in the Lybian Desert to the westward. 

 Schweinfurth has found a rock of similar aspect in hills near 

 the Red Sea, where it appears to have been quarried. The 

 description given by Arzruni of the variety found at Abu 

 Zabel closely corresponds with that of Mr. Adams quoted above. 



This kind of rock, probably because of its accessibility and 

 abundance, or perhaps because of the good polish of which it 

 is capable, and the slight play of colours of the felspar and 

 olivine when seen in a bright light, was much used for small 

 objects, especially in Lower Egypt. As examples of this, 1 

 have in my collection a palette for grinding colours, a polisher, 

 a perforated disk, two scarabs, some beads, and one of the 

 sacred eyes used as charms. Statues and ornamental work 

 in temples seem also to have been made of it ; but it is not 

 well suited to long exposure to the weather, as the olivine 

 and augite are acted on by the atmosphere, and become rusty. 



