Heat treatment of an Egyptian natural diatomite was performed at different temperatures (600, 900, 1000, 1100, and 1200oC). The samples were heated from room temperature 23±1^oC to the appointed temperature at a rate of 20^oC/ min, and kept at that temperature for 5 hour. The heat treated samples were examined by X-ray diffraction, scan- electro-microscopy, and other physical characters like sample color, texture, and weight reduction. Results showed that heat treatment of natural diatomite caused different forms of mineral modification and transformation to another mineral. At 1200^oC a new nano-metric silicate material was formed. These changes were mainly depending upon the treated temperature, diatomite genera, and the accompanied gangue minerals as well.