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Questions and Answers
What is the defining characteristic of the triclinic crystal system?
What is the defining characteristic of the triclinic crystal system?
- All crystallographic axes are of equal length
- All crystallographic axes are perpendicular
- None of the crystallographic angles are equal to 90 degrees (correct)
- The point of intersection of the three axes is called axial cross
In the orthorhombic crystal system, what is the relationship between the lengths of the crystallographic axes?
In the orthorhombic crystal system, what is the relationship between the lengths of the crystallographic axes?
- Two crystallographic axes are equal in length, while one is different
- All crystallographic axes are equal in length
- None of the crystallographic axes are equal in length (correct)
- The crystallographic axes form a right angle with each other
Which crystal system is also known as the Isometric system?
Which crystal system is also known as the Isometric system?
- Monoclinic system
- Triclinic system
- Hexagonal system
- Cubic system (correct)
What is the relationship between the crystallographic angles in the hexagonal system?
What is the relationship between the crystallographic angles in the hexagonal system?
What is a characteristic of the monoclinic crystal system in terms of its angles?
What is a characteristic of the monoclinic crystal system in terms of its angles?
Which crystal system has all crystallographic axes being non-perpendicular?
Which crystal system has all crystallographic axes being non-perpendicular?
What is unique about the lengths of the crystallographic axes in the hexagonal system?
What is unique about the lengths of the crystallographic axes in the hexagonal system?
How many crystallographic angles are equal to 90 degrees in the orthorhombic system?
How many crystallographic angles are equal to 90 degrees in the orthorhombic system?
Which crystal system has three unequal crystallographic axes forming a right angle with each other?
Which crystal system has three unequal crystallographic axes forming a right angle with each other?
In which crystal system are all three crystallographic axes mutually perpendicular?
In which crystal system are all three crystallographic axes mutually perpendicular?
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Study Notes
Crystal Systems Overview
- Crystals can be classified into different systems based on their symmetrical properties and axes.
- Each system has its unique characteristics regarding rotation axes, mirror planes, and mineral species.
Orthorhombic System
- Possesses three 2-fold rotation axes and/or three mirror planes.
- The holomorphic class includes three 2-fold symmetry axes, three mirror planes, and a center of inversion.
- Other classes may contain different combinations of these features.
- Mineral species include olivine and barite.
- Common crystal habits: prismatic, tabular, or acicular.
Monoclinic System
- Characterized by three unequal axes; two are inclined to each other at an oblique angle, while the third is perpendicular to the other two.
- The two vertical axes do not intersect at right angles.
- Displays a single 2-fold rotation axis and/or a single mirror plane.
- The holomorphic class has a single 2-fold rotation axis, a mirror plane, and a center of symmetry.
- Mineral species include pyroxene, amphibole, orthoclase, azurite, and malachite.
- Common crystal habit: long prisms.
Triclinic System
- Defined by three unequal axes intersecting at oblique angles; no axes are perpendicular.
- Possesses only a 1-fold symmetry axis, indicating minimal symmetry presence, with no mirror planes.
- The holomorphic class features a center of inversion symmetry.
- Mineral species include plagioclase and axinite, typically exhibiting a tabular habit.
Crystal Forms
- A crystal form is defined as a set of geometrically equivalent faces related by the crystal's symmetry.
- Specifying one face defines the point symmetry operations that inform the crystal's class and its other faces.
- In the isometric or cubic system, there are fifteen different forms, including:
- Hexoctahedron
- Gyroid
- Hextetrahedron
- Diploid
- Tetartoid
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