Particle
a minute quantity or solid fragment, not necessarily of uniform composition. Particle size, quantity and characteristics (composition, shape, surface features, color, etc.) are all important factors considered in a total fluid analysis. A particle’s visual characteristics may be described generically. They may also have specific terms associated with them, especially when certain wear modes are under examination. With respect to characteristics, selected particle types and/or surface features are:
| Fine | An extremely small fragment, very thin in gauge or texture. |
| Sliver | A long slender piece cut or torn off. |
| Flake | A thin flattened piece or layer. Chip is also used for this type particle, with the connotation of features associated with sudden sharp impact or a regular process such as machining. |
| Granule | A small grain-like form, usually but not always crystalline. |
| Clump | A compact mass of smaller forms grouped together. |
| Chunk | A short thick piece. |
| Sphere | A rounded globular body. |
| Fiber | A slender and greatly elongated threadlike natural or synthetic filament. |
| Smooth | A continuous even surface, free of irregularities. |
| Rough | Having definite inequalities, ridges, or projections. |
| Pitted | Marked with small regular hollows or indentations. |
| Jagged | A sharply uneven edge or surface. |
| Striated | Marked with a series of shallow parallel grooves, lines or channels. |
| Furrowed | Marked with deep wrinkles or rough-edged ‘plowed’ grooves. |
| Ridged | Marked with raised strips or elongated crests. |
| Oxidized | A surface dulled or damaged by the chemical combination of oxygen with the material composing the particle. |
| Corroded | Agressively eaten away and/or weakened by direct chemical action. |
| Reflective | Bouncing or returning light from a surface. |
| Refractive | Permitting the passage of light but bending or changing its direction. |
| Opaque | Absorbing light; obstructing or preventing its passage. |
| Translucent | Permitting the passage of light, but diffusing it so interior features and opposite-side surface features of the particle cannot clearly be seen. |
| Transparent | Transmitting light without significant scattering or redirection, so that all surface and interior features of the particle and objects beyond it are clearly visible. |