It is slightly translucent to almost opaque, sometimes only thin chips are translucent at the edges. The color can be caused by inclusions of organic compounds (black), metal sulfides (black), and various metal oxides and hydroxides (yellow, orange, brown, reddish, etc.). Flint may show color banding, but this is not a concentric banding as seen in agate. ![]() If a large body of rock is entirely made of dense, dull cryptocrystalline quartz, it is generally called chert, regardless of its color. Brighter or more colorful variants are sometimes called chert by some people. ![]() It is possible that once I've been working through the literature more deeply I change my mind and lump chert, flint (and possibly jasper) together.įlint does not have a specific color, but is often dark gray with shades of brown, red, or yellow, and sometimes white. This is done not so much out of respect for the "tradition", but because I'm not sure how "special" flint is in its properties, and how broadly the term chert is defined with respect to structural and physical properties. However, I will use the term "flint" for the nodular forms and the term "chert" for the rock-forming type. In that sense, Knauth did the right thing to call flint "nodular chert", because he considers them equal in their basic physical properties. Otherwise the nomenclature will turn quickly into a inconsistent mess, once old assumptions about the formation must be revised. Knauth, 1994) refer to flint as "nodular chert".Īs a general rule, one should primarily categorize rocks according to what they are, and not to how they formed. This chapter is called "Flint and Chert", but after looking at the matter again and again, I'm getting less and less convinced that chert and flint should be treated together in a chapter, although some authorities on that matter (e.g. ![]() There's apparently no clearly defined line that separates flint from chert and that people agree on. Both terms are more often used very broadly. Others use the term "flint" for nodules and "chert" for large bodies of rocks. Some authors use "chert" as the more general term, with flint being a dark variant. Firestone, Hornstone, and Silex are other names for flint and chert. Flint and chert are dense, cryptocrystalline varieties of quartz, slightly translucent to almost opaque.
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