Name/Title
ThomsoniteEntry/Object ID
78.63.434Description
Chemical Composition: NaCa2Al5Si5O20-6H2O
Crystal System: Orthorhombic System
Description: Common Name: Thomsonite
Group Name: Silicates
Chemistry: NaCa2Al5Si5O20-6H2O
Location: Lake Superior
Description: This is a small piece that they get in Lake Superior. Colors: Light green, grey and
yellowish. It has been polished.
Physical Characteristics:
• Luster is vitreous.
• Transparency: Crystals are transparent to translucent.
• Crystal System is orthorhombic.
• Crystal Habits include tight acicular radiating clusters and sphericules. Blocky, prismatic, fibrous and tabular crystals are also known.
• Cleavage is perfect.
• Fracture is uneven.
• Hardness is 5 - 5.5
• Specific Gravity is approximately 2.2 - 2.4 (light).
• Streak is white.
• Associated Minerals are quartz, calcite, chabazite, natrolite, heulandite, stilbite and other zeolites.
• Notable Occurrences include Saxony, Germany; Italy; Faroe Islands; Kilpatrick Hills, Scotland and Kern Co., California and Cape Lookout, Oregon, USA.
• Best Field Indicators are crystal habit, density, hardness and associations.
Fracture: Uneven
Hardness: 5 Apatite
Luster: Vitreous
Occurrence: Thomsonite is one of the rarer zeolites. It forms tight acicular radiating clusters and sphericules as well as some blockier crystals that are found in the vesicles or bubbles of volcanic rock as are most other zeolites. Natrolite , another zeolite , is usually square in cross section but is otherwise difficult to distinguish from thomsonite. The color is usually colorless or white, but a few specimens have shown a lovely yellow color. Thomsonite is a rare mineral and is sought after by collectors of rare zeolite minerals.
Zeolites are known to have an openness about their structure that allows large ions and molecules to reside and actually move around inside the overall framework. The structure actually contains open channels that allow water and large ions to travel into and out of the crystal structure. The size of these channels controls the size of the molecules or ions and therefore a zeolite can act as a chemical sieve, allowing some ions to pass through while blocking others.
Rock Type: Sedimentary
Specific Gravity: 2.2 -2 .4
Streak: whiteCollection
Delmar Smith Crystal CollectionDimensions
Width
1 inDepth
1/2 inLength
3/4 inDimension Notes
Dimension taken at widest pointsLocation
Location
Shelf
CS-E-1Room
Curation StorageBuilding
Crater Rock MuseumCategory
StorageMoved By
CuratorDate
February 23, 2024
