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2. Geode - Wikipedia

   en.wikipedia.org/wiki/Geode

   Quartz-filled geode, shown from inside (top) and outside (bottom) A geode (/ ˈ dʒ iː. oʊ d /; from Ancient Greek γεώδης (geṓdēs) 'earthlike') is a geological secondary formation within sedimentary and volcanic rocks. Geodes are hollow, vaguely spherical rocks, in which masses of mineral matter

3. Igneous rock - Wikipedia

   en.wikipedia.org/wiki/Igneous_rock

   For textural classification, igneous rocks that have crystals large enough to be seen by the naked eye are called phaneritic; those with crystals too small to be seen are called aphanitic. Generally speaking, phaneritic implies an intrusive origin or plutonic, indicating slow cooling; aphanitic are extrusive or volcanic, indicating rapid cooling.

4. List of rock types - Wikipedia

   en.wikipedia.org/wiki/List_of_rock_types

   Phosphorite – Sedimentary rock containing large amounts of phosphate minerals – A non-detrital sedimentary rock that contains high amounts of phosphate minerals; Sandstone – Type of sedimentary rock; Shale – Fine-grained, clastic sedimentary rock; Siltstone – Sedimentary rock which has a grain size in the silt range

5. Igneous textures - Wikipedia

   en.wikipedia.org/wiki/Igneous_textures

   Phaneritic (phaner = visible) textures are typical of intrusive igneous rocks, these rocks crystallized slowly below Earth's surface. As magma cools slowly the minerals have time to grow and form large crystals. The minerals in a phaneritic igneous rock are sufficiently large to see each individual crystal with the naked eye.

6. Amethyst - Wikipedia

   en.wikipedia.org/wiki/Amethyst

   An amethyst geode that formed when large crystals grew in open spaces inside the rock. The largest amethyst geode found as of 2007 was the Empress of Uruguay, found in Artigas, Uruguay in 2007. It stands at a height of 3.27 meters, lies open along its length, and weighs 2.5 tons. Amethyst is also found and mined in South Korea. [19]

7. Volcanic rock - Wikipedia

   en.wikipedia.org/wiki/Volcanic_rock

   Phenocrysts are crystals that are larger than the matrix and are identifiable with the unaided eye. Rhomb porphyry is an example with large rhomb shaped phenocrysts embedded in a very fine grained matrix. [4] Volcanic rocks often have a vesicular texture caused by voids left by volatiles trapped in the molten lava.