Alumina powder

An alumina powder, comprising:

• a hydroxycarboxylic acid;
• and
• an alkaline component,
• the alumina powder containing amorphous alumina, pseudoboehmite, or boehmite,
• wherein the alumina powder satisfies all of (1) to (4):
• (1) a colloidal dispersion A with 2.5% by mass of Al2O3 consisting of the alumina powder and distilled water is free from precipitate, and the colloidal dispersion A has a light transmittance of at least 80% measured at a wavelength of 500 nm and an optical path length of 10 mm,
• (2) a colloidal dispersion B with 15% by mass of Al2O3 consisting of the alumina powder and distilled water is free from precipitate,
• (3) the colloidal dispersion A and the colloidal dispersion B each have a pH in a range of 5 to 8, and
• (4) a colloidal dispersion C with 2.5% by mass of Al2O3 consisting of the alumina powder and methanol is free from precipitate, and the colloidal dispersion C has a light transmittance of at least 80% measured at a wavelength of 500 nm and an optical path length of 10 mm.