An abrasion-resistant dielectric composite product is described comprising a substrate and an abrasion wear resistant coating material comprising carbon, hydrogen, silicon, and oxygen and a dielectric material. An improved method is provided for the deposition of highly durable and abrasion-resistant multilayer dielectric antireflective coatings and reflective colored mirror coatings onto plastic lenses such as ophthalmic lenses, safety lenses, sunglass lenses, and sports optics. An adhesion-enhancing polymer layer may be deposited onto the plastic substrate prior to deposition of the abrasion-resistant first coating layer. The multilayer dielectric coating structure consists of a transparent, highly abrasion-resistant first coating, and a second dielectric coating composed of at least one layer of dielectric material. The abrasion-resistant first coating layer is deposited by ion-assisted plasma deposition from mixtures of organosiloxane or organosilazane precursor gases and oxygen, and has the properties of Nanoindentation hardness in the range of about 2 GPa to about 5 GPa, a strain to microcracking greater than about 1.5% and less than about 3.5%, a transparency greater than 85% throughout the visible spectrum, and an abrasion resistance greater than or equal to the abrasion resistance of glass. The preferred method for deposition of the abrasion-resistant first coating layer is plasma ion beam deposition using an organosiloxane precursor gas and oxygen. Optimum abrasion-resistance is obtained when the first coating layer thickness is in the range of about 5 microns to about 20 microns. The thickness, refractive index, and number of the dielectric layers in the second coating are chosen to produce the desired optical effects of either antireflection, or reflected color. Optimum environmental durability and abrasion-resistance is obtained by producing highly dense dielectric coatings by ion beam assisted electron beam evaporation, magnetron sputtering, ion beam assisted magnetron sputtering, ion beam sputtering, and ion-assisted plasma deposition, including plasma ion beam deposition, from precursor gases.