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English: Fluorine worlds are hypothetical planetary environments where fluorine-rich conditions prevail, potentially leading to unique geological and climatic characteristics. This concept is based on the understanding that fluorine, though relatively rare in the universe, is enriched in Earth's crust and has interesting chemical properties that may have implications for habitability.Fluorine is the 24th most abundant element in the universe, making up about 4× 10−5% of all elements. On Earth, it is more abundant, ranking as the 13th most abundant element by weight percent in the crust (0.054%), just ahead of carbon. Fluorine shares a high affinity with common elements such as silicon, aluminum, calcium, and magnesium, which are also abundant in Earth's crust and the universe. Consequently, fluorine is found bound within stable substances, especially outside liquid conditions.While fluorine's chemical properties make it an alternative substitute for oxygen, the latter is far more abundant both in the universe and Earth's crust. Oxygen plays a central role in the chemistry of life on Earth, while fluorine, despite being present in the crust, appears to be largely ignored by the biosphere as a building block for life. This is likely due to the rarity of metabolically generated fluorinated compounds, as well as the low availability of fluorides in solution compared to other elements like oxygen and chlorine.Fluorine gas is pale yellow or yellow-green in color when observed in large quantities. The yellow color is a result of the absorption and emission of specific wavelengths of light by the fluorine molecules. In gaseous form, fluorine exists as a diatomic molecule, where two fluorine atoms are bonded together. In its liquid state, it will not have the yellow-green color that is observed in its gaseous form. Instead, fluorine liquid would be a clear, transparent substance with no visible color.No fluorine planets have yet been observed or discovered. The concept of "fluorine planets" is purely hypothetical and theoretical, based on scientific discussions about the possibility of life in fluorine-rich environments and the potential uses of fluorine in alternative biochemistry.Since no fluorine planets have been observed or studied, it is not possible to determine their appearance or color as viewed from space. In reality, the color of a planet depends on various factors, including its composition, atmosphere, and the nature of its surface.Planets in our solar system, for example, exhibit a wide range of colors due to different surface features, atmospheres, and chemical compositions.