There are 300 Ore Crystals to be found in Red Faction: Guerrilla. When you smash them all, a trophy/achievement will be awarded.
It is unknown what element the particular veins of ore are depicted in Guerrilla. It is largely depicted as being found in small surface deposits. It is likely a valuable mineral resource for developing the local Martian economy, but not necessarily for exports to the Earth market. It is predominately mined by independent prospectors and contractors such as Alec Mason rather than large Earth-based corporations. However, larger and more difficult to extract veins will be sought aggressively by these business giants with forceful, cronyist backing of the EDF.
The ore requires a relatively complex refining process for practical applications. There are two such minor processing plants in Parker where prospectors can sell their mined ore. One is an independent, locally owned venture while the other is controlled by the EDF and attempts to act as an inefficient and enforced monopoly over the marketplace. There are larger, corporate owned refineries in Dust where the majority of Mars' raw materials are extracted.
Ore Crystals are similar to buildings in a way: they release Salvage after being destroyed. Each Crystal will release 2 pieces of Ore, each piece worth 5 Salvage (6 salvage with Ore Additive upgrade). Taken that the player does purchase the Ore Additive upgrade, collecting all 300 Ore Crystals will award the player 3600 Salvage.