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  2. Tourmaline - Wikipedia

    en.wikipedia.org/wiki/Tourmaline

    Rarely, it can be found as neon green or electric blue. Tourmaline ( / ˈtʊərməlɪn, - ˌliːn / TOOR-mə-lin, -⁠leen) is a crystalline silicate mineral group in which boron is compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone comes in a wide variety of colors.

  3. Hornfels - Wikipedia

    en.wikipedia.org/wiki/Hornfels

    Hornfels. Hornfels is the group name for a set of contact metamorphic rocks that have been baked and hardened by the heat of intrusive igneous masses and have been rendered massive, hard, splintery, and in some cases exceedingly tough and durable. [1] These properties are caused by fine grained non-aligned crystals with platy or prismatic ...

  4. Pleochroism - Wikipedia

    en.wikipedia.org/wiki/Pleochroism

    Pleochroism is an extremely useful tool in mineralogy and gemology for mineral and gem identification, since the number of colors visible from different angles can identify the possible crystalline structure of a gemstone or mineral and therefore help to classify it. Minerals that are otherwise very similar often have very different pleochroic ...

  5. Sandstone - Wikipedia

    en.wikipedia.org/wiki/Sandstone

    Typically quartz and feldspar; lithic fragments are also common. Other minerals may be found in particularly mature sandstone. Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains, cemented together by another mineral. Sandstones comprise about 20–25% of all sedimentary rocks.

  6. Charoite - Wikipedia

    en.wikipedia.org/wiki/Charoite

    Charoite (/ tʃ æ r oʊ. aɪ t / CHAR-ow-ait) is a rare silicate mineral with the chemical composition K(Ca,Na) 2 Si 4 O 10 (OH,F)•H 2 O, first described in 1978.It is named after the Chara River, despite its being 70 kilometres (43 mi) away from the discovery place.

  7. Tourmaline Surfing Park - Wikipedia

    en.wikipedia.org/wiki/Tourmaline_Surfing_Park

    Tourmaline Surfing Park is a beach access point and surfing spot in North Pacific Beach, a community of San Diego, California. The park is situated at the northern end of Pacific Beach, a short distance south of where the sand beach ends and the rocky promontory of La Jolla begins. There are cliffs to the north and south of Tourmaline Surfing ...

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