Glassing

Glassing is the act of using high-energy weapons to bombard a planetary surface, which is melted in the immense heat, turning the silicate minerals on the upper layer of the crust into a glass-like mineraloid known as lechatelierite. While historically applied to intense nuclear bombardment, glassing is now more commonly associated with the Covenant practice of using starship-borne plasma weapons to bombard a planetary surface.

The Covenant do not glass planets for practical or strategic reasons, as the process is about as far from practical as one can get. Not only is devastating inhabitable planets wasteful and inefficient, but there are faster ways to go about it. Once they have established orbital superiority, the Covenant could simply point a hypervelocity impactor at the planet to render it uninhabitable in a much shorter amount of time than it takes to commit to planetary glassing. However, glassing has a special religious importance to the Covenant, representing the most ultimate form of purification, a burning away of sin and corruption. Indeed, when applied on a large scale, glassing is more of a religious ritual than a military one. Its main strategic and political role is in its demoralizing effect and setting an example.

Depending on the number of ships committed to the glassing, fully rendering an Earth-like planet uninhabitable can take months, even years. This represents a substantial commitment of energy, time, and resources, especially with fleets operating far from the heartlands of the Covenant Sphere. As long as a fleet is committed to a planetary glassing, it cannot move on to other targets, and has to contend with counterattacks. This was common throughout the Human-Covenant War, though more so in the early years, with the five-year Harvest Campaign being a notable example. In some cases where multiple human colonies were discovered in a short span of time, the Covenant would carry out rapid intersystem attacks to eliminate the UNSC forces present in the sector, and only then proceed to methodically glass those worlds completely.

As the war progressed, many Covenant fleets settled for glassing the major population centers before moving on when it came to most human colonies. Full planetary glassing was reserved for worlds whose destruction was deemed by religious officials to warrant special "purification". This was frowned upon by some Sangheili fleetmasters, who saw such acts as wasteful. Even in such cases, deep oceans were rarely glassed in their entirety as this would take prohibitively long amounts of time. Even if the entirety of the planet's surface is not subjected to bombardment, secondary effects of glassing (radiation, ash and dust in the atmosphere, wildfires, climate shifts) will typically render a planet hostile to human life.

Glassing is rarely employed in intra-Covenant conflicts and is heavily restricted under the rules of Shal'annu, though it is sometimes used to set an example against rebellions or splinter groups deemed heretical or apostate. Even then, the full glassing of Covenant worlds is rare due to the strategic value of those worlds; more often, cities or bases are targeted with tactical glassing.

Since the end of the war, re-terraforming of glassed worlds has become relevant. Fully glassed planets may take well over a century to reclaim, while some colonies that only suffered localized glassing may be recoverable within years.