An abrasive grain is disclosed and may include a body. The body may define a length (l), a height (h), and a width (w). In a particular aspect, the length is greater than or equal to the height and the height is greater than or equal to the width. Further, in a particular aspect, the body may include a primary aspect ratio defined by the ratio of length:height of at least about 2:1. The body may also include an upright orientation probability of at least about 50%.

An abrasive grain is disclosed and may include a body. The body may define a length (l), a height (h), and a width (w). In a particular aspect, the length is greater than or equal to the height and the height is greater than or equal to the width. Further, in a particular aspect, the body may include a primary aspect ratio defined by the ratio of length:height of at least about 2:1. The body may also include an upright orientation probability of at least about 50%.

An abrasive grain is disclosed and may include a body. The body may define a length (l), a height (h), and a width (w). In a particular aspect, the length is greater than or equal to the height and the height is greater than or equal to the width. Further, in a particular aspect, the body may include a primary aspect ratio defined by the ratio of length:height of at least about 2:1. The body may also include an upright orientation probability of at least about 50%.

An abrasive grain is disclosed and may include a body. The body may define a length (l), a height (h), and a width (w). In a particular aspect, the length is greater than or equal to the height and the height is greater than or equal to the width. Further, in a particular aspect, the body may include a primary aspect ratio defined by the ratio of length:height of at least about 2:1. The body may also include an upright orientation probability of at least about 50%.

An abrasive grain is disclosed and may include a body. The body may define a length (l), a height (h), and a width (w). In a particular aspect, the length is greater than or equal to the height and the height is greater than or equal to the width. Further, in a particular aspect, the body may include a primary aspect ratio defined by the ratio of length:height of at least about 2:1. The body may also include an upright orientation probability of at least about 50%.

The present invention provides alumina particles having a fixed card-house structure formed of three or more flat plate-like alumina particles and having an average particle diameter of 3 to 1000 μm. Also, there is provided alumina particles having an average particle diameter of 3 to 1000 μm and having a fixed card-house structure in which the three or more flat plate-like alumina are aggregated to be crossed each other at two or more plurality of positions, and the plane directions of the flat plates crossed each other are in a state of disordered arrangement.

Plate-like alumina particles have an aspect ratio of 5 to 500, in which in solid-state .sup.27Al NMR analysis, the longitudinal relaxation time T.sub.1 for a peak of six-coordinated aluminum at 10 to 30 ppm is 5 seconds or more at a static magnetic field strength of 14.1 T.

Plate-like alumina particles have an aspect ratio of 5 to 500, in which in solid-state .sup.27Al NMR analysis, the longitudinal relaxation time T.sub.1 for a peak of six-coordinated aluminum at 10 to 30 ppm is 5 seconds or more at a static magnetic field strength of 14.1 T.

An abrasive grain is disclosed and may include a body. The body may define a length (l), a height (h), and a width (w). In a particular aspect, the length is greater than or equal to the height and the height is greater than or equal to the width. Further, in a particular aspect, the body may include a primary aspect ratio defined by the ratio of length:height of at least about 2:1. The body may also include an upright orientation probability of at least about 50%.

To provide plate-like alumina particles that are less likely to wear apparatuses. Plate-like alumina particles containing germanium or a germanium compound. The plate-like alumina particles preferably have a molar ratio of Ge to Al, [Ge]/[Al], of 0.08 or more as determined in an XPS analysis. The plate-like alumina particles preferably contain the germanium or germanium compound in a surface layer. The plate-like alumina particles preferably have a density of 3.7 g/cm.sup.3 or more and 4.1 g/cm.sup.3 or less. The plate-like alumina particles preferably have a molar ratio of Ge to Al, [Ge]/[Al], of 0.08 or less as determined in an XRF analysis.