Pattern in Islamic Art

Qur'an fragment (Timurid Samarkand) attributed to Umar Aqta

Please wander through this amazing website, created by David Wade:
PATTERN in ISLAMIC ART

especially the page on the Religious Origins & Significance of the Decorative Arts in Islam

also good are the TOAH essays on

Calligraphy in Islamic Art
Geometric Patterns in Islamic Art

and

Vegetal Patterns in Islamic Art

Also very good is this page on Arts of the Islamic World at the Freer / Sackler website

Mosque Lamp of Sayf al Din (7-29) British Museum 

Carpet Fragment (Mughal Kashmir or Lahore)

Also on ArtStor 

Tile from the Alcazar in Seville, Spain