Growth Features

Growth features are internal patterns formed during crystallization. Unlike solid
or fluid inclusions which are "foreign" material, growth features are intrinsic
to the crystal's development and reflect changing conditions during formation.

Colour zoning results from variations in trace element concentration during growth:

Formation:

• Changes in fluid chemistry during crystallization
• Different growth faces incorporate elements at different rates
• Temperature or pressure fluctuations

Types:

• Straight zoning - Parallel bands following crystal faces
• Angular zoning - Follows hexagonal or other crystal geometry
• Irregular zoning - Patchy, non-geometric distribution
• Sector zoning - Different colours in different growth sectors

Hollow channels formed parallel to the crystal's c-axis during growth:

Characteristics:

• Elongated, tube-like cavities
• Usually parallel to main growth direction
• May contain fluid or be empty
• Can create "rain-like" appearance

Common in:

• Tourmaline (very characteristic)
• Aquamarine (parallel tubes)
• Some garnets (rare)

Twinning occurs when crystal lattices join in specific orientations:

Types:

• Contact twins - Two crystals joined at a plane
• Penetration twins - Crystals interpenetrate
• Polysynthetic twins - Multiple parallel twin planes

Appearance under magnification:

• Reflection planes visible internally
• Interference colours under polarized light
• Step-like features at twin boundaries

Phantom inclusions show earlier growth stages preserved inside the crystal:

Formation:

• Crystal growth temporarily stops
• Surface accumulates dust or mineral coating
• Growth resumes, encasing earlier form

Appearance:

• Ghost-like outline of earlier crystal
• Often shows different colour or clarity
• Demonstrates crystal's growth history

Common in:

• Quartz (chlorite or iron oxide phantoms)
• Fluorite (colour change phantoms)
• Occasionally in other minerals

Internal graining results from structural irregularities during growth:

Types:

• Whitish graining - Light-coloured lines or planes
• Reflective graining - Shiny internal reflections
• Coloured graining - Associated with colour distribution

Most significant in diamonds:

• Affects clarity grading
• Can indicate plastic deformation
• May show strain patterns

Visible under crossed polarizers, strain patterns reveal internal stress:

Causes:

• Rapid temperature changes during formation
• Pressure from included crystals
• Tectonic stress during geological history

Observation:

• Best seen with polarized light
• Appears as interference colours
• Patterns radiate from stress sources