Tachylite is a rare volcanic glass that forms through the rapid cooling of molten lava. Although there aren't many synonyms for the word tachylite, some related terms include basaltic glass, volcanic obsidian, and pitchstone. Basaltic glass is a similar type of volcanic glass that forms in the same way as tachylite, but it has a slightly different chemical composition. Volcanic obsidian is another type of volcanic glass that forms when lava cools rapidly, and it is often used in jewelry and other decorative items. Lastly, pitchstone is a type of volcanic glass that has a lower silica content than tachylite, and it often appears brown or black in color.