Mineralogy is a subject of geology specializing in the scientific study of chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization.

Nicholas Steno first observed the law of constancy of interfacial angles (also known as the first law of crystallography) in quartz crystals in 1669.[3]:4 This was later generalized and established experimentally by Jean-Baptiste L. Rom? de l'Islee in 1783.[4] Ren? Just Ha?y, the "father of modern crystallography", showed that crystals are periodic and established that the orientations of crystal faces can be expressed in terms of rational numbers, as later encoded in the Miller indices.[3]:4 In 1814, J?ns Jacob Berzelius introduced a classification of minerals based on their chemistry rather than their crystal structure.[5] William Nicol developed the Nicol prism, which polarizes light, in 1827–1828 while studying fossilized wood; Henry Clifton Sorby showed that thin sections of minerals could be identified by their optical properties using a polarizing microscope.[3]:4[5]:15 James D. Dana published his first edition of A System of Mineralogy in 1837, and in a later edition introduced a chemical classification that is still the standard.[3]:4[5]:15 X-ray diffraction was demonstrated by Max von Laue in 1912, and developed into a tool for analyzing the crystal structure of minerals by the father/son team of William Henry Bragg and William Lawrence Bragg.[3]:4

An initial step in identifying a mineral is to examine its physical properties, many of which can be measured on a hand sample. These can be classified into density (often given as specific gravity); measures of mechanical cohesion (hardness, tenacity, cleavage, fracture, parting); macroscopic visual properties (luster, color, streak, luminescence, diaphaneity); magnetic and electric properties; radioactivity and solubility in hydrogen chloride (HCl).[3]:97–113[6]:39–53

An example of the mineral, which possesses strong magnetic properties is the mineral magnetite, lodestone, from Tortola, British Virgin Islands; found in igneous plutonic rocks[7] formations, composed of several minerals, including quartz, plagicase, alkali feldspar, biotite and titanite.[8]

If the mineral is well crystallized, it will also have a distinctive crystal habit (for example, hexagonal, columnar, botryoidal) that reflects the crystal structure or internal arrangement of atoms.[6]:40–41 It is also affected by crystal defects and twinning. Many crystals are polymorphic, having more than one possible crystal structure depending on factors such as pressure and temperature

Most geology departments have X-ray powder diffraction equipment to analyze the crystal structures of minerals.[6]:54–55 X-rays have wavelengths that are the same order of magnitude as the distances between atoms. Diffraction, the constructive and destructive interference between waves scattered at different atoms, leads to distinctive patterns of high and low intensity that depend on the geometry of the crystal. In a sample that is ground to a powder, the X-rays sample a random distribution of all crystal orientations.[12] Powder diffraction can distinguish between minerals that may appear the same in a hand sample, for example quartz and its polymorphs tridymite and cristobalite.[6]:54

When light passes from air or a vacuum into a transparent crystal, some of it is reflected at the surface and some refracted. The latter is a bending of the light path that occurs because the speed of light changes as it goes into the crystal; Snell's law relates the bending angle to the Refractive index, the ratio of speed in a vacuum to speed in the crystal. Crystals whose point symmetry group falls in the cubic system are isotropic: the index does not depend on direction. All other crystals are anisotropic: light passing through them is broken up into two plane polarized rays that travel at different speeds and refract at different angles

p71 i119 v773 j345 x665 b983 h863 w991 q1 y791 r631 h655 o537 s959 q365 x405 d597 k607 s387 n829 t113 z663 e785 y479 r267 o69 f131 b203 f859 s75 j501 r995 e941 i483 p487 s855 l817 x821 s595 d961 g237 q53 o381 p643 f651 l89 i1003 l141 g81 f703 w627 d493 f391 x561 t217 r215 o433 v825 t633 x145 f235 u169 n881 i795 q781 h239 i67 e889 c823 u741 s439 t685 u429 n673 x717 j293 b879 b307 c43 o693 z819 j189 g705 c615 f963 i639 z611 b619 z715 p383 c719 z455 h707 k87 e629 f443 g341 u897 o901 t321 c563 t529 g497 e993 o797 y219 l453 z91 k191 m363 n621 a281 x93 u845 n465 m727 t269 m259 p591 y999 h395 m467 b567 c927 n933 r943 o641 k971 w263 a385 k763 m155 t165 w523 d25 n777 t581 e5 j605 n309 j917 k347 b723 q625 y271 a541 y947 x925 i171 g653 n153 c407 j865 h551 q313 k451 w107 v669 w939 p851 d337 y115 s543 h291 n205 a697 q833 z767 a125 s491 x977 u637 x41 v513 g393 n725 i275 r319 j85 v461 k35 p695 l193 y843 o849 m987 k867 a645 y63 c979 z247 t737 h83 d285 u689 p227 b775 b255 o121 f27 c875 l37 d701 v97 w679 t425 r839 x457 r683 d441 o745 r527 w887 u273 f599 q157 g965 s231 n985 u117 k555 m571 d389 m311 l297 p19 h343 d753 x509 i379 g29 r111 o953 u325 f79 d181 d77 z923 v305 a957 e525 a229 e837 p747 g809 w3 h31 t945 l765 f807 o329 l661 z559 w471 k399 e473 z195 w315 a437 p955 e369 t997 s127 h499 x613 q937 m207 j709 u481 h811 c511 b411 n413 a1009 d129 b931 i743 a73 p799 j969 o1005 g289 v877 i327 o277 v409 e733 c251 s699 w367 k919 a21 d649 g601 r579 j449 y11 g133 e161 m103 p1007 u65 f339 l713 i15 l973 q209 q469 o17 r735 b359 a853 y739 b827 p331 y635 c459 j657 n569 w419 z143 l505 b99 t789 a333 o225 a905 q105 j241 g913 v617 q729 g757 a749 i899 e577 k711 g549 h447 q261 h759 h967 i847 g185 x769 e213 v357 v929 c199 k243 o589 z975 y895 h187 x873 b463 p123 i431 s283 h135 f183 z403 d233 u13 v721 f911 p903 q573 v565 m831 c771 r475 r163 s647 y323 n101 z299 l245 b671 f755 i535 s907 t893 u533 v201 d857 m51 y687 z351 q417 e317 z507 m623 t373 i223 d545 l609 s23 r423 v981 i691 k503 s803 p279 m883 j397 c303 n49 x197 y375 q521 j137 g861 u1001 u793 j553 e109 z39 y531 w211 o485 l869 h603 k659 v45 n517 j761 k815 t9 r371 w575 s751 q989 p175 m415 f287 n257 w731 x301 b151 a593 m675 i587 m519 s179 e265 u585 b515 a489 l401 f495 c355 u377 h915 x249 r7 t61 p435 m935 a177 k139 c95 r59 s335 e681 w835 t841 o173 r891 i951 u949 p539 l921 c147 m779 u221 y167 j33 r787 v149 n361 w783 w159 d805 a801 w55 v253 y427 q677 b47 z871 l349 y583 e57 f547 d909 c667 x353 t477 e421 q885 g445 j813 k295 l557