Silicon carbide (SiC) was synthesized through the carbothermal reduction of mineral-derived silicon dioxide (SiO₂) using an argon-assisted vacuum route, establishing a direct link between natural mineral resources and functional ceramic nanomaterials. The obtained β-SiC nanostructures, with crystallite sizes of 13–44 nm depending on strain relaxation, were incorporated into a polystyrene (PS) matrix (1–10 wt %) to investigate how filler morphology and loading affect the composite’s optical and dielectric behavior. X-ray diffraction confirmed the cubic 3C-SiC phase, while SEM revealed faceted micrograins derived from SiO₂ precursors. FTIR spectra retained the characteristic polymer bands but showed progressive enhancement of Si–O–C and Si–C vibrations, confirming partial surface oxidation typical of mineral-origin SiC. Optical spectroscopy indicated a widening of the band gap from 3.91 to 4.22 eV as SiC concentration increased up to 5 wt %, reflecting improved dispersion and cleaner SiC–PS interfaces. Dielectric spectroscopy revealed a systematic rise in permittivity (ε′) and controlled energy dissipation (ε″) with filler loading, governed by Maxwell–Wagner–Sillars interfacial polarization below percolation. The composite with 7 wt % SiC exhibited the highest crystallinity and minimal internal strain, demonstrating an optimal balance between dielectric stability and optical transparency. This study bridges mineral-based precursor chemistry and polymer nanocomposite design, offering a sustainable route for developing multifunctional dielectric and UV-shielding materials from naturally sourced SiO₂.