Patent ID: 8785010

Claim:
A magnetic disk glass substrate, wherein an arithmetic mean roughness (Ra) of a polished main surface of the glass substrate measured using an atomic force microscope with a resolution of 256×256 pixels in a 2 μm×2 μm square is 0.12 nm or less and, among defects detected to have a size of 0.1 μm or more and 0.3 μm or less upon irradiating light with a wavelength of 405 nm onto the glass substrate with a spot size of 5 μm and detecting scattered light from the glass substrate, the number of the defects fixed to the glass substrate, whose position on the glass substrate is not changed before and after the glass substrate is immersed for 200 seconds in the dilute sulfuric acid solution adjusted to pH4, is 1 or less per 24 cm 2 , wherein the glass substrate is an amorphous aluminosilicate glass, and wherein a ratio (Ra/Rp) of the arithmetic mean roughness (Ra) to a maximum peak height (Rp) on the main surface of the glass substrate is 0.15 or more.