Prehnite is best recognized by its characteristic apple-green color and distinct botryoidal or globular habit. It is commonly found as a secondary mineral in the vesicles and cavities of mafic volcanic rocks and is a popular choice for cabochons due to its attractive luster and durability.
Spotting prehnite in the field
Field marks- 1
Pale green to yellow-green, translucent, with a distinctive grape-cluster botryoidal surface
- 2
Interior shows a radiating fibrous structure
- 3
Hardness 6 to 6.5, with a slightly waxy to pearly luster
Prehnite fills cavities in basalt and other volcanic rock, so the places to look are traprock quarries and lava flows. The New Jersey traprock quarries around Paterson are the classic American locality, alongside the Keweenaw in Michigan and the Bay of Fundy basalts in Nova Scotia. The botryoidal grape-cluster surface with a radiating interior is very distinctive, and prehnite frequently hosts fine needles of black epidote, which collectors specifically want.
Straight answers
- Is it worth cutting?
- Cabs well and its slightly cloudy translucence suits a high dome. Specimens with black epidote needles inside are worth cutting to display the needles.
- What is it really worth?
- Inexpensive. Translucent even green material, and pieces with sharp epidote inclusions, carry the premium.
- Can you legally keep it?
- Active traprock quarries are private and generally allow collecting only through organized club visits, which is the practical route in New Jersey.
Often confused with
Prehnite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Chrysoprase is chalcedony at hardness 7 with conchoidal fracture. Prehnite is softer and shows a radiating fibrous interior.
How to tell apart: Also botryoidal, but usually blue-white rather than green, and softer at 4.5 to 5.
Often found alongside prehnite
Minerals reported to co-occur with prehnite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂Al₂Si₃O₁₀(OH)₂
- Mohs hardness
- 6-6.5
- Density
- 2.8-3.0 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Botryoidal, Globular, Reniform, Or Tabular Crystals
- Cleavage
- Distinct On {001}
- Rarity
- Common
- Uses
- Collector, Lapidary, Ornamental
- Host rock
- Basaltic Volcanic Rocks and Hydrothermal Veins
- Typical price
- $5-50 for specimens, $10-100 for high-quality polished stones
Where rockhounds find prehnite
28 mapped spotsClassic worldwide localities
- South Africa
- Mali
- United States
- Canada
- Australia
U.S. states with prehnite
Each link opens a state-specific list of mapped rockhounding spots that produce prehnite.
Field-hunting tip
Look in basaltic volcanic rocks and hydrothermal veins country, the host setting where prehnite typically forms. If you start seeing datolite, calcite, epidote in float, you are in the right ground. Field specimens usually show a botryoidal, globular, reniform, or tabular crystals habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in New Jersey, Michigan, Connecticut. Start trip planning there.
Common questions
How do you identify prehnite?+
Where is prehnite found?+
Can I find prehnite in the United States?+
How much is prehnite worth?+
What rocks look like prehnite?+
What minerals are found with prehnite?+
What kind of rock does prehnite form in?+
What is prehnite used for?+
Find prehnite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
