2506 - Quartz (other than natural sands); quartzite, whether or not roughly trimmed or merely cut, by sawing or otherwise, into blocks or slabs of a rectangular (including square) shape:

Chapter 25 of the Harmonized Tariff Schedule (HTS) broadly encompasses mineral products, including various types of salt, sulfur, earths, and stone. Within this chapter, heading 2506 specifically identifies quartz and quartzite. This category covers natural quartz in its raw or processed forms, excluding natural sands, as well as quartzite, which is a metamorphic rock composed predominantly of quartz. The classification includes these materials whether they are roughly trimmed or simply cut into blocks or slabs of a rectangular or square shape.

Distinguishing heading 2506 from its sibling categories within Chapter 25 requires focusing on material composition and form. For instance, unlike heading 2507 (Other's clay) or 2516 (Stone, rough stones and worked stone, other than marble, travertine and alabaster, of the foregoing:), which deal with different types of minerals or stone, 2506 is precisely defined by its quartz content. It also differs from headings covering manufactured goods derived from these minerals, as it pertains to the raw or semi-processed mineral product itself.

Heading 2506 is further subdivided to differentiate between quartz and quartzite. Subheading 2506.10.00 specifically covers "Quartz," encompassing the mineral silicon dioxide in its crystalline form, which can be utilized in various industrial and technological applications. Subheading 2506.20.00 is dedicated to "Quartzite," a durable rock formed from metamorphosed sandstone. This distinction is important for customs purposes as the end uses and commercial values of pure quartz and quartzite can differ.