The projected shape of a particle is its transmitted light outline. These shapes can be very helpful in determining the type of particle present. Fibers are an obvious example. The shape alone eliminates a huge range of possibilities. One of the first steps in keying out a pollen grain is to classify its outline. Shape, as used here, is distinct from angularity or roundness. Those are details handled later in this section.

Circles may be the result of a liquid deposition or a growth pattern. The projected shape is not sufficient to determine if the particle is spherical.

Pollens come in many shapes and vary in size from a few micrometers to hundreds of micrometers. Most are in the range of 15 to 100 micrometers. The wall of a pollen grain consists of at least two distinct layers and as many as four distinct layers that may be separated by characteristic pillar structures.

Spores come in many shapes but tend to be smaller than most pollens, often have a visible attachment point, and a single layer membrane wall.

Diatoms can be divided into two broad types, Pennate and Centric, though there are also intermediate shapes. Pennate diatoms are elongated, have one axis much longer than the other two. Centric diatoms have one shorter axis and the other two are similar giving the diatom a circular or slightly ellipsoidal shape.

Phytoliths have their own catalog of shape descriptors that is unique.

Tapered cylinders are created by a unidirectional force. In the case of tire wear it is the friction of the tire against the road. In the case of some combustion sources it is the shrinkage created by the advancing thermal gradient.

Globular particles are particles with internal and external centers of curvature over their surface.

Straight edges indicate a linear structural element that may be a cleavage surface, a growth pattern or a linear force that generated the particle.

Rosettes are the result of growth outward from a central nucleation point.

Dendrites are branching structures were the trunk and the branches have the same diameter. These are common as a result of electrostatic deposition, some chemical reactions, and some skeletal crystal growth habits.