• A non-crystalline material (amorphous solid) is one where the measured X-ray powder diffraction (XRPD) pattern is essentially continuous in appearance.
• Amorphous don’t have a definite form it is non-crystalline in nature.
• Silica glass is called amorphous glasses when they have not had time to crystallize on cooling.
• Silica glass is complex and contains many different substances which have different crystalline states.
• The melting range of a glaze is dictated by the different melting points of the constituents and their interaction with one another in eutectic combinations.
• The glaze becomes a liquid which on cooling becomes an amorphous solid.

• Crystallinity refers to the degree of structural order in a solid.
• High-density polyethylene (HDPE) and low-density ethylene (LDPE) are a class of polymers.
• Low density polythene has less crystallinity.
• The presence of chain branching will tend to reduce the possibility of an ordered arrangement and so reduce the crystallinity.
• For example, the crystallinity of LDPE (low-density polyethylene) usually varies between 55% and 70%, compared with 75%-90% for HDPE (high density polyethylene).
• Semi-crystalline materials have a highly ordered molecular structure with sharp melt points.
• They do not gradually soften with a temperature increase, instead, semi-crystalline materials remain solid until a given quantity of heat is absorbed and then rapidly change into a low viscosity liquid.

High density, long-range of order, the sharp diffraction pattern is a characteristic of crystalline structure.

• A crystalline structure has a very close packing of atoms thus giving rise to high density to the material it possesses when compared to its non-crystalline form.
• For example, quartz is the crystalline form of silica has a density of about 2.65 gm/cm³, whereas its ally–non-crystalline form silica glass has a density of 2.20 gm/cm³.
• For reference, the other properties being differentiated between crystalline and non-crystalline forms are tabulated below.

In a non-crystalline structure, there is no definite packing of atoms, which makes them possess any random shape, further these atoms are being bonded by weak secondary bonds with Van der Wall’s forces, thus giving a low density of the material.

Characteristics of non-crystalline structure

• The materials of non-crystalline structure are having an irregular pattern of ions, molecules, or atoms.
• The melting point is not fixed. It is over a range of temperatures.
• There is no definite heat fusion.
• The density of the material is low.
• Examples include Glass and asphalt.
• These materials are also called isotropic so require a higher force of indentation and are having a higher brittle nature

• A strong secondary bond is not responsible for the formation of a non-crystalline structure.
• A non-crystalline structure is formed by secondary bonds and molecular bonds are formed as a result of weak Van der Wall’s attractions which exist between various atoms.
• These intermolecular bonds can be further classified as dispersion bonds, dipole bonds, hydrogen bonds, which are all should be considered as weak secondary bonds.

The simplest and most symmetric crystal is the cubic (or isometric) system. This has the symmetry of cube, i.e., all the three axes are mutually perpendicular and of equal length (a = b = c, α = β = γ = 90°). Common cubic crystals are diamond, gold, spinel, etc.

a = b = c, α = β = γ = 90° axis system is being satisfied by cubic crystal system.

The tetragonal result from stretching a cubic lattice along with one of its lattice vectors, so that the cube becomes a rectangular prism with a square base (a by a) and height (c, which is different from a).

The tetragonal crystal will have a square base and top, but a taller height. All the three axes should be at the right angle, i.e. α = γ =  β = 90° and two basis vectors must be of equal length a = b ≠ c

a = b ≠ c, α = β = ϒ = 90° axis system is being satisfied by tetragonal crystal system.

The orthorhombic system resulted from stretching a cubic lattice along with two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base and height. All three bases intersect at 90 degrees angles. The three lattice vectors remain mutually orthogonal.

All the three axes are perpendicular to each other with unequal lengths, i.e.

α = γ =  β = 90° and a ≠ b ≠ c axis system is being satisfied by the orthorhombic crystal system

Rhombohedral is known as the trigonal crystal system. The rhombohedral system can be thought of as the cubic system stretched diagonally along a body. This crystal is described by vectors of equal length and all the three axes are not mutually perpendicular, i.e.,

a = b =c and α = γ =  β ≠ 90° axis system is being satisfied by rhombohedral (trigonal) crystal system.

The hexagonal crystal system has four crystallographic axes. Three of the four axes are in one plane, intercept at 120°, and are of the same length. The fourth is either longer or shorter but must be at a right angle toward the other corners. In brief,

α = β = 90°, γ = 120° and a = b ≠ c axis system is being satisfied by the hexagonal crystal system