Crystal habit
|
|
In mineralogy, shape and size give rise to descriptive terms applied
to the typical appearance, or habit of crystals.
The many terms used by mineralogists to describe crystal habits are
useful in communicating what specimens of a particular mineral often
look like. Recognising numerous habits helps a mineralogist to
identify a large number of minerals. Some habits are distinctive of
certain minerals, although most minerals exhibit many differing
habits which are influenced by certain factors. Crystal habit may
mislead the inexperienced as a mineral's crystal system can be
hidden or disguised.Factors influencing a crystal's habit
include: a combination of two or more forms; trace impurities
present during growth; crystal twinning and growth conditions (i.e.,
heat, pressure, space). Minerals belonging to the same crystal
system do not necessarily exhibit the same habit. |
Some habits of a mineral are unique to its variety and locality: For
example, while most sapphires form elongate barrel-shaped crystals,
those found in Montana form stout tabular crystals. Ordinarily, the
latter habit is seen only in ruby. Sapphire and ruby are both
varieties of the same mineral; corundum.
Some minerals may replace other existing minerals while preserving
the original's habit: this process is called pseudomorphous
replacement. A classic example is tiger's eye quartz, crocidolite
asbestos replaced by silica. While quartz typically forms euhedral
(well-formed), prismatic (elongate, prism-like) crystals, in tiger's
eye the original fibrous habit of crocidolite is preserved.
List of crystal habits
Habit: Description: Example:
Acicular - Needle-like, slender and/or tapered - Rutile in quartz
Amygdaloidal - Almond-shaped - Heulandite
Anhedral - Poorly formed, distorted - Olivine
Bladed - Blade-like, slender and flattened - Kyanite
Botryoidal or globular - Grape-like, hemispherical masses -
Smithsonite
Columnar - Similar to fibrous: Long, slender prisms often with
parallel growth - Calcite
Coxcomb - Aggregated flaky or tabular crystals closely spaced. -
Barite
Dendritic or arborescent - Tree-like, branching in one or more
direction from central point - Magnesite in opal
Dodecahedral - Dodecahedron, 12-sided - Garnet
Drusy or encrustation - Aggregate of minute crystals coating a
surface - Uvarovite
Enantiomorphic - Mirror-image habit and optical characteristics;
right- and left-handed crystals - Quartz
Equant, stout, stubby or blocky - Squashed, pinnacoids dominant over
prisms - Zircon
Euhedral - Well-formed, undistorted - Spinel
Fibrous or columnar - Extremely slender prisms - Tremolite
Filiform or capillary - Hair-like or thread-like, extremely fine -
Natrolite
Foliated or micaceous - Layered structure, parting into thin sheets
- Mica
Granular - Aggregates of anhedral crystals in matrix - Scheelite
Hemimorphic - Doubly terminated crystal with two differently shaped
ends. - Hemimorphite
Mamillary - Breast-like: intersecting large rounded contours -
Malachite
Massive or compact - Shapeless, no distinctive external crystal
shape - Serpentine
Nodular or tuberose - Deposit of roughly spherical form with
irregular protuberances - Geodes
Octahedral - Octahedron, eight-sided (two pyramids base to base) -
Magnetite
Plumose - Fine, feather-like scales - Mottramite
Prismatic - Elongate, prism-like: all crystal faces parallel to
c-axis - Tourmaline
Pseudo-hexagonal - Ostensibly hexagonal due to cyclic twinning -
Aragonite
Pseudomorphous - Occurring in the shape of another mineral through
pseudomorphous replacement - Tiger's eye
Radiating or divergent - Radiating outward from a central point -
Pyrite suns
Reniform or colloform - Similar to mamillary: intersecting
kidney-shaped masses - Hematite
Reticulated - Acicular crystals forming net-like intergrowths -
Cerussite
Rosette - Platy, radiating rose-like aggregate - Gypsum
Sphenoid - Wedge-shaped - Sphene
Stalactitic - Forming as stalactites or stalagmites; cylindrical or
cone-shaped - Rhodochrosite
Stellate - Star-like, radiating - Pyrophyllite
Striated/striations - Surface growth lines parallel or perpendicular
to c-axis - Chrysoberyl
Tabular or lamellar - Flat, tablet-shaped, prominent pinnacoid -
Ruby
Wheat sheaf - Aggregates resembling hand-reaped wheat sheaves -
Zeolites |
 |
|
Nofeerentals.com Apartment rental NY NYC, Rental apartments in New York city Nofeerentals.com has rental apartments and provides no fee apartment rental in downtown Manhattan New York City near New York University and all Manhattan http://www.nofeerentals.com/index.asp
Notasinc.com Window Balconies, hand made carved wood balconies These handicrafts are a beautifully hand made wood balconies, crafted by in Colombia by artisans with quality materials and a distinct original design. The Wood is used in every part of each piece, including the individually carved roof tiles. http://www.notasinc.com/window_balconies.htm
Jewelheaven.com: gemstone pendant color stone pendant blue sapphire pendant set birthstone pendants blue sapphire pendant ruby pendants gemstone pendant color stone pendants and pendant set. http://www.jewelheaven.com/pendant.asp
Lansend.com: Microsoft Certified Computer consultants in New York, NY Microsoft Certified Computer consultants providing computer and network consulting services in New York ,NY Manhattan Queens, Lan Wan Networking VPN. http://www.lansend.com
Microfiber futon cover suede futon cover jaguar animal print futon cover
Suede Jaguar Futon Cover microfiber futon cover is a suede futon cover with
jaguar animal print. futon covers are machine washable futon covers
http://www.futonstogo.com/details-of-product/futon-cover-micro-suede-jaguar-suede-theme.asp
|