These structures are created by colonies of micro-organisms and are found in several sectors. including Sanguineous Rim and The Abyss, mostly around the outer edge of the galaxy (see in-game Codex for locations). There appears to be only a single classification of crystalline shards. They spawns the usual range of raw materials, though they seem to spawn more high grade materials than most other types of site. They are distinct from most biological findings in that they tend to be found alongside geological activity (such as vents and campfires) which can be active. The crystal shards are tall vertical crystals apparently created by large colonies of micro-organisms. They appear among the geological features (which also have harvest-able materials).
Scan them with the ship or SRV Composition Scanner to record them in your codex for further details on where they can appear.
(Image: CMDR Clusternuke)