Compressed particles, or stacked particles are made by turning off gravity, making a block of Powder, pausing and dragging it off screen using the crosshairs (mac)/move(windows) tool. Unpause it, and a line of powder will shoot across the screen. After it has touched the other side of the screen, pause again, and drag it off screen in the opposite axis you just did (e.g. If you dragged it horizontally, drag it vertically now). A single compressed particle of powder should appear, and if you look at it in Blob or shader mode, it will be a huge circle.
Compressed particles are basically a bunch of particles squeezed into the space of one. Another name for them, stacked particles, refers to the fact that all of the particles within are overlaid and act as one object until they hit something. You can make compressed particles any element by simply using Replace with your desired material selected. They are also formed "naturally" (under default Parameters) by Tensile in globs that achieve a certain size, and have a single point in the center, surrounded by a dense symmetrical grouping of neighboring particles. However, the point density of these emergent c-particles is seen to be much less (at most 3 or 4) than those made by Stacking or the Powder block compression methods, which in theory could approach infinite density.
Compressed (non-Rigid) particles make excellent "missiles" because they are small, but their explosive power is only limited by how many particles are in them.
They make good "mines", because they only explode when something touches them, or they touch something else.
Compressed particles made of Powder + Inflow can be a powerful explosive.
Rigid Compressed particles also are good for use in heavy projectiles, because they exert a huge force on anything they touch, and can be used in a device called a Compressed Particle Gun, which uses a point-wide channel in Wall to act as both a reflective well that keeps the solid C-Particle vibrating between the sides, and a loading mechanism where the high-frequency vibration slows the fall of the projectile, so it can properly press down at some certain angle (most often found by trial and error, and multiple modifications to the lower mechanisms) on a Rigid bar laying on top of another Rigid piece (usually denser, or combined with Axis)that stabilizes it, allowing the projectile an exit out of the gun.