Video on Instagram This large red-colored Topaz is from a famous San Luis Potosi locality. Rutile inclusions cause of the color and the outstanding ones have consistent inclusions all-the-way through making them a saturated “iron-red” color. The matrix of this piece is an altered-rhyolite tuff (fallen hot-ash) from the Sierra Madre Occidental. The Topaz grew in miarolitic vugs and cavities within the alter tuff units produced by the large caldera systems nearby. The Rutile is a result of a Ti component in the ash. The contrast between the matrix and the crystal overshadows the ding on the corner of the termination. The Mina Veronica material typically has a prismatic termination like this one. Other altered rhyolite Topaz specimens typically have pinacoidal termination like the ones from the Thomas Range in Utah. This 3 cm crystal is enormous for this style of deposit and is an outstanding example of this classic Mexican material.