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螢石，又稱氟石、砩石，是氟化鈣（CaF2）的礦物形式。它屬於鹵化物礦物。儘管八面體和更複雜的等距形式並不少見，但它以立方晶系結晶。螢石通常通過熱液活動在長英質火成岩中形成為晚結晶礦物。它在花崗偉晶岩中尤為常見。它可能作為通過熱液活動形成的礦脈沉積物出現，特別是在石灰岩中。純螢石在可見光和紫外光下都是無色透明的，但雜質通常使其成為彩色礦物，並且具有觀賞和寶石用途。螢石有多種顏色，因此被稱為「世界上最豐富多彩的礦物」。最常見的顏色是紫色、藍色、綠色、黃色或無色。不太常見的是粉紅色、紅色、白色、棕色和黑色。螢石的顏色由雜質、輻射暴露和色心空洞等因素決定。
Known for its wide variety of colors, fluorite is a common mineral deposited in veins 礦脈, fractures 裂縫 and cavities 洞穴 by hydrothermal processes. Fluorite's colors, including the Blue John variety with bands of purple, blue and yellow, are caused by impurities or exposure to radiation. Other sources of color, known as color centers, are defects in the crystal structure that become filled with rare-earth elements, like yttrium 釔.