Name/Title
Stilbite on ApophylliteEntry/Object ID
2009.62.73Description
Chemical Composition: see description
Crystal System: Hexagonal System
Description: Common Name: Apophyllite / Stilbite
Chemistry: (K,Na)Ca4Si8O20(F,OH) - 8H2O, Hydrated Potassium Calcium Sodium Silicate / NaCa2Al5Si13O36 -14H2O, Hydrated sodium calcium aluminum silicate Fluoride Hydroxide
Group: Zeolites
Location: Jalgaon, India
Description: Small specimen with translucent white crystals of various sizes clustered on a base, with a single Stilbite crystal, pink in color imbedded on it. The matrix is brown with worm-like striations across it, light brown in color.
PHYSICAL CHARACTERISTICS OF APOPHYLLITE:
Color is clear, white, green, yellow, pink, violet or rarely brown.
Luster is vitreous to pearly on cleavage surfaces.
Transparency: Crystals are transparent to translucent.
Crystal System is tetragonal; 4/m 2/m 2/m; natroapophyllite is orthorhombic, 2/m 2/m 2/m.
Crystal Habits include four sided prisms (with a square cross-section) truncated with either a steep four sided pyramid or a pinacoid termination or both. If the pyramids are missing, the crystals can look cubic. Rarely are the prisms missing, but if they are, crystals could appear octahedral because of the four sided pyramids. The faces of the pyramids do not lineup with the prism faces but with their edges, therefore the pyramid faces have four edges and appear diamond shaped instead of triangular like the pyramid faces of quartz. Rare tabular hydroxyapophyllite crystals are also known.
Cleavage is perfect in one direction (basal).
Fracture is uneven.
Hardness is 4.5 - 5.
Specific Gravity is approximately 2.3 - 2.4 (lighter than most translucent minerals).
Streak is white.
Other Characteristics: Prism faces are striated lengthwise, some specimens are fluorescent and crystals will flake when heated.
Associated Minerals are prehnite, quartz, heulandite, stilbite, natrolite, analcime, datolite, babingtonite, cavansite, calcite, idocrase, wollastonite, kinoite, gyrolite and many other zeolites.
Best Field Indicators are crystal habit, striations, associations, environment of formation, cleavage and luster on cleavage surfaces.
PHYSICAL CHARACTERISTICS OF STIBITE:
Color is pink or white; also tinted yellow and red.
Luster is vitreous to pearly especially on the prominant pinacoid and cleavage surfaces.
Transparency: crystals are transparent to mostly translucent.
Crystal System is monoclinic; 2/m
Crystal Habits include platy often thin crystals that can aggregate together into a wheat sheaflike structure. The prominant pinacoid is sometimes but rarely modified by other pinacoid and prism faces. Cruciform (cross-like) twins can also be found. Also forms radiating nodules.
Cleavage is perfect in one direction parallel to the prominant pinacoid.
Fracture is uneven.
Hardness is 3.5 - 4.
Specific Gravity is approximately 2.2 (very light)
Streak is white.
Associated Minerals are quartz, calcite, babingtonite, apophyllite, heulandite, natrolite and other zeolites.
Best Field Indicators are crystal habit, luster, density and associations.
Fracture: conchoidal
Hardness: 3 Calcite
Luster: Vitreous
Occurrence: Apophyllite is found in the voids in the contact metamorphic zone limestones that surround intrusive rocks.
Stilbite commonly forms nice crystals inside the petrified bubbles (called vesicles) of volcanic rocks that have undergone a small amount of metamorphism.
Apophyllite specimens are found in ancient lava and basalt flows. The crystals grow in the now solid cavities, called amygdules or vesicles, formed by air bubbles when the rock was molten.
Rock Type: Metamorphic
Specific Gravity: 2.7
Streak: white
Variety: The name apophyllite is derived from the Greek apophylliso, meaning "it flakes off," a reference to this class's tendency flake apart when heated, due to water loss.
Stilbite crystals can aggregate together to form a structure resembling wheat sheafs. This hourglass structure looks like several crystals stacked parallel to each other with the tops and bottoms of this structure fanning out while the middle remains thin. Stilbite's hallmark crystal habit is unique to stilbite and a rarer but related zeolite called stellerite. Whether in the wheat sheafs or not, stilbite can be a hansome specimen with its pearly luster and often colorful pink tints.Collection
RAGM Mineral CollectionAcquisition
Accession
2009.62Source or Donor
Museum Collection of MineralsAcquisition Method
DonationDimensions
Weight
10.82 ozDimension Notes
Dimension taken at widest pointsLocation
Location
Display Case
FS-11Room
Frieda Smith HallBuilding
Crater Rock MuseumCategory
PermanentMoved By
Curtis GardnerDate
May 25, 2023Notes
Added current location