obsidian

Obsidian is a naturally occurring volcanic glass formed when felsic lava erupts or extrudes and rapidly cools, preventing crystalline growth. It is typically dark in color, ranging from black to dark brown or green, with a smooth, glassy luster. Its composition is high in silica, and it fractures conchoidally, producing very sharp edges. Historically, obsidian was valued for its ability to be chipped into precise tools and weapons, and it was widely used by prehistoric cultures for blades, scrapers, and points. Obsidian deposits occur in numerous volcanic regions around the world, including parts of the Americas, Europe, and the Near East. Varieties such as snowflake obsidian, which contains feldspar inclusions that resemble snowflakes, and rainbow obsidian, which shows iridescent surfaces from microstructural features, are notable. In jewelry and decorative objects, obsidian is cut and polished into pieces such as cabochons and beads.

Obsidian (software) is a note-taking and knowledge-management application that organizes plain text Markdown files stored locally on a user’s device. It supports bidirectional linking between notes, backlinking, and a graph view to visualize relationships among ideas. Core features include search, tags, templates, and support for plugins and themes to customize functionality. The software emphasizes a local-first approach, enabling offline use and data portability, while offering optional cloud synchronization through its own service or third-party providers. Obsidian runs on Windows, macOS, Linux, iOS, and Android, and is widely used for personal knowledge management, research, and writing workflows.