The Virgin Mary mosaics are in the interior of the half dome of the apse and are made on a golden background. Mary is portrayed here as sitting on a throne with no back for reclining, and studded with precious stones. The Virgin is pictured here as wearing a dark lapis lazuli garment, and holding the Child Jesus on her lap. Her feet are rested on a pedestal embellished with precious stones. Mary's face was very successfully portrayed, as regards to both the lines and the diffusion of colours.
On the great arch of the apse, there used to be an inscription saying: "The pictures that were spoiled some time ago by imposters, were made again by capable and pious emperors. "
Today only the fIrst three, and the last nine letters of this inscription are visible. Here, by referring to importers, the image-bereaking Iconoclasts must be implied. As understood from this inscription, and from the speech delivered by Patriarch Photius on March 29, 867, the Virgin Mary mosaics were partially destroyed during the Iconoclasm movement, and have been made once more right after the termination of this movement. These mosaics are the oldest in Hagia Sophia. Although the Virgin Mary mosaics belong to the Ninth Century, the golden mosaics in the background date back from the Sixth Century
Above text and pictures are from the book titled "Hagia Sophia".
You can purchase "Hagia Sophia" book and other Turkey related books from Explore Turkey Bookstore.