Crystals are like snowflakes in the sense that no two are exactly the same. The way a crystal or a group of crystals looks, including its shape, is called its “habit.” And these vary significantly because factors like temperature and pressure play a huge role in how a crystal forms. So, when you see a crystal, its unique “habit” tells you a story about where and how it grew.
In this article, we’re going to list a few examples of some of the different types of crystal growth along with examples of each one.
1. Needlelike or “Acicular”
Acicular crystals are characterized by their slender, needle-like appearance. This form typically arises in environments where rapid growth occurs along one crystallographic axis, often due to high supersaturation levels of the mineral components in the solution.
This scolecite on quartz specimen is a classic example of a crystal with radiating needles.
2. Botryoidal
This chalcopyrite specimen grows outward from the center which results in rounded nodules that look like “grape clusters” or “botryoidal. This formation occurs when numerous small, radiating crystals grow simultaneously, often in environments where mineral-rich solutions precipitate onto surfaces, such as the walls of cavities or fractures.
3. Prismatic
Prismatic crystals are elongated in one direction, forming prism-like shapes. This habit typically develops in environments where the crystal’s growth rate is significantly higher along one axis compared to the others, often due to anisotropic conditions during crystallization.
4. Coralloid
Coralloid crystals resemble coral structures, often forming in environments with rapid precipitation from mineral-rich solutions, such as cave settings where minerals like aragonite (pictured above) precipitate from dripping water.
5. Specular
Specular crystals are characterized by their shiny, mirror-like surfaces. This habit often occurs in minerals like hematite, where the crystal faces are smooth and reflect light efficiently, typically forming in high-temperature environments such as hydrothermal veins.
6. Equant
Equant crystals are those whose length, width, and depth dimensions are approximately equal, making them appear roughly the same size in all directions, similar to a sphere or cube. This habit indicates uniform growth rates along all crystallographic axes, often occurring in stable environments with consistent temperature and pressure conditions. Garnets are a great example of this formation.
7. Foliated
Foliated minerals are characterized by layers or sheets, which give them a leaf-like appearance. This structure is typical of minerals such as mica, which can be split into thin, flexible sheets.
8. Phantom Growth
Phantom growth is when there appears to be a crystal within a crystal due to where earlier stages of growth are encapsulated by later ones. These “phantoms” show up as ghostly outlines or layers within the crystal. This occurs often in quartz.
9. Hopper Growth
Hopper growth is characterized by a skeletal or hollowed-out crystal structure, where the edges grow faster than the centers of crystal faces. This habit typically forms in environments with rapid crystallization, such as evaporating saline solutions, leading to incomplete filling of the crystal lattice.
10. Dendritic
Dendritic crystal growth resembles branching tree patterns, often seen in minerals like manganese and iron oxides that form in fractures or solutions.
11. Cubic
Cubic crystal habit refers to crystals that grow into shapes with six square faces, each face meeting at right angles, resembling a cube. This growth form is characteristic of minerals like pyrite and halite.
