Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
9 Cards in this Set
- Front
- Back
|
origin
|
minerals can be formed in various ways. some crystallize from molten magma and gases of the earth's interior or from volcanic lava streams that reach the earth's surface (igneous or magmatic minerals). Others crystallize from hydrous solutions or grow with the help or organisms on or near theearth's surface (sedimentary minerals). Lastly, newminerals are formedby recrystallization of existing minerals under great pressure andhigh temperatures inthe lower regions of the earth's crust (metamorphic minerals)
|
|
|
Crystal systems
|
in crystallography, crystals are divided into seven systems. the distinction is made according to crystal axes and the angles at which the axes intersect.
|
|
|
cubic system
|
all three axes have the same length and intersect at right angels. typical crystal shapes are the cube, octahedron, rhombic dodecahedron, pentagonal dodecahedron, icosi-tetrahedron, and hexicisochedron
|
|
|
tetragonal system
|
the three axes intersect at right angels, two areof the same length and are in the same plane, while the main axis is either longer or shorter. typical crystal shapes are four-sided prisms and pyramids, trapezohedrons and eight-sided pyramids as well as double pyramids
|
|
|
hexagonal system
|
three of the four axes are in one plane, are of the same length, and intersect each other at angels or 120 degrees. the fourth axis which is a different length, is at right angels to the others. typical crystal shapes are hexagonal prisms and pyramids, as well as twelve-sided pyramids and double pyramids
|
|
|
trigonal system
|
three of four axes are int he same plane, ar eof equal length, and intersect each other at angles of 120 degrees. The fourth axis, which is of different length, is at right angels to the others. The difference is one of symmetry. In the case of the hexagonal system, the cross section of the prism base is six-sided; in the trigonal system, it is three-sided. the six-sided hexagonal shape is formed by a cutting-ooff process of the corners of the triangles. typical crystal forms of the trigonal system are three-sided prisms and pyramids, rhombohedra, and scalenohedra.
|
|
|
orthorhombic system
|
three axes of different lengths are at right angles to each other. typical crystal shapese are basal pinacoids, rhombic prisms, and pyramids as well as rhombic double pyramids
|
|
|
monoclinic system
|
the three axes are each of different lengths; two are right angles to each other, andthe third one is inclined. Typical rystal forms are basal pinacoids and prisms with inclined end faces.
|
|
|
triclinic system
|
all three axes are of different lengths and inclined to each other. typical crystal forms are paired faces
|
