Thomsonite-Sr is a member of the zeolite group most frequently collected for its beautiful radiating, fibrous, and often multi-colored banded patterns in volcanic rock vesicles. It is typically found as radial sprays of needle-like crystals or dense botryoidal masses which polish exceptionally well for lapidary use.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineraluncommonZeolite Group family

Thomsonite-Sr

Hardness: 5
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this thomsonite-sr?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch thomsonite-sr with a known reference. Thomsonite-Sr sits at Mohs 5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: colorless.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: prismatic.

Often confused with

Thomsonite-Sr vs. its common look-alikes, and how to tell them apart in the field.

Often found alongside thomsonite-sr

Minerals reported to co-occur with thomsonite-sr. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: NaSr₂Al₅Si₅O₂₀·6-7H₂O
Mohs hardness: 5
Density: 2.47 g/cm³
Colors: Colorless
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Orthorhombic
Crystal habit: Prismatic
Cleavage: Perfect on {100} and good on {010}
Rarity: Uncommon
Uses: Collector, Lapidary
Host rock: In hydrothermal veinlets that cut the natrolite-bearing core of a pegmatite in an alkaline massif

Where rockhounds find thomsonite-sr

Classic worldwide localities

Mt. Rasvumchorr and Mt. Yuksporn, Khibiny massif, Kola Peninsula, Russia

Field-hunting tip

Where it forms: In hydrothermal veinlets that cut the natrolite-bearing core of a pegmatite in an alkaline massif. If you start seeing microcline, aegirine, annite in float, you are in the right ground. Typical habit: prismatic. Train your eye for that shape before scanning the outcrop.

More thomsonite-sr photos

Common questions

How do you identify thomsonite-sr?+

Mohs hardness is 5. Luster: vitreous. The streak is white. Common colors include colorless.

Where is thomsonite-sr found?+

Notable localities include Mt. Rasvumchorr and Mt. Yuksporn, Khibiny massif, Kola Peninsula, Russia.

What rocks look like thomsonite-sr?+

Thomsonite-Sr is most often confused with Mesolite, Natrolite, Scolecite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with thomsonite-sr?+

Thomsonite-Sr commonly co-occurs with Microcline, Aegirine, Annite, Astrophyllite, Magnetite, Fluorapatite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does thomsonite-sr form in?+

Where it forms: In hydrothermal veinlets that cut the natrolite-bearing core of a pegmatite in an alkaline massif. Working float back to the host body is the standard way to chase a fresh occurrence.

What is thomsonite-sr used for?+

Thomsonite-Sr is used in collector, lapidary.

Find thomsonite-sr on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.