## 4 Results and Discussion  
### Sample Petrographic Description  
The massif of the Aswan region consists of granitic rocks of the Precambrian age, the earlier phases of which are more mafic, coarse-grained, and sometimes show porphyritic and rapakivi textures. The K-feldspar megacrysts show intensive perthitization of an evolution origin and occur in more than one generation, sometimes replacing each other. The K-feldspar includes oriented plagioclase crystals that lie parallel to the re-entrant angles at the Carlsbad twinning planes of the K-feldspar megacrysts. The plagioclase megacrysts also contain oriented biotic, magnetite, and apatite inclusions that are concentrated in the cores and between the cores and their outer rims. Occasionally, these include crystals lying parallel to the re-entrant angles at the Carlsbad twinning planes of the plagioclase megacrysts. These features suggest crystallization of the K-feldspar and plagioclase megacrysts from silicate melts and lend some support to the magmatic hypothesis of the Aswan batholith. Aswan granite is composed mainly of alkali-feldspars, plagioclase, quartz, biotite, and hornblende. Zircon, allanite, epidote, titanite, and opaques are the main accessory minerals. The studied granites are generally light grey with a reddish tone. The rocks are equigranular and exhibit a phaneritic texture. The main constituents are quartz (20-35%), K-feldspar (up to 50%), plagioclase (10-25%) and subordinate biotite \(\pm\) amphibole (5-16%). Quartz is observed in the rocks as medium- to coarse-grained, occurring as anhedral crystals. Minute quartz crystals occupy the interstitial spaces between feldspars. The potash feldspars are the main constituents and represented by perthite, microcline perthite, orthoclase perthite, and microcline. Perthite occurs as subhedral crystals and has both albite and pericline twinning, which form a known tartan pattern (Figure 2a). Some crystals of perthite include the second phase of biotite (Figure 2b). Microcline perthite occurs as an anhedral crystal associating plagioclase (Figure 2c) and sometimes includes crystals of zircon (Figure 2d). Orthoclase perthite occurs as euhedral to subhedral crystals showing simple twinning; sometimes, some crystals of orthoclase perthite are found enclosing the second phase of albite (Figure 2e). Exsolution textures are commonly represented by perthite and equilibrium quartz-feldspar intergrowth (i.e., myrmekite). Figure 2: _Cont._  
Plagioclase is represented by subhedral to euhedral prismatic crystals of variable sizes with distinct lamellar twinning (Figure 2f). Myrmekite texture is developed at the margins of plagioclase and microcline (Figure 2g). Some plagioclase crystals are oscillatory zoned (Figure 2h). It is coarse to very coarse grains which are digested and mantled by perthite (Figure 3a), referring to the mixing magma. Epidotization and muscovitization are the main alteration product of plagioclase (Figure 3b,c). The plagioclase exsolution lamellae are large enough to exhibit the characteristic polysynthetic twinning pattern (parallel stripes). In contrast, the K-feldspar host displays splendid \"tartan\" or \"cross-hatched\" twinning. Figure 3: _Cont._  
Figure 2: Photomicrographs for Aswan granite showing: (**a**) Subhedral crystal of perthite of tartan type, CN. (**b**) Second phase of biotite in perthite, CN. (**c**) Anhedral crystal of microcline perthite associating plagioclase, CN. (**d**) Well-formed crystal of zircon associating quartz and microcline perthite, CN. (**e**) Subhedral crystal of orthoclase perthite enclosing second phase of albite, CN. (**f**) Euhedral crystal of plagioclase with lamellar twining associating perthite, CN. (**g**) Anhedral crystals of plagioclase with vermicular of quartz (myrmikitic) on the border of string perthite, CN. (**h**) Zoned crystal of plagioclase associating albitic plagioclase, quartz and biotite, CN. The mafics are represented by biotite, muscovite and hornblende.