Glauconite is a characteristic green mica mineral typically found as dull, granular pellets in marine sedimentary rocks. It is highly valued by geologists as an indicator of slow depositional rates in shallow marine environments and is commonly associated with sandstones and limestones.
Is this glauconite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch glauconite with a known reference. Glauconite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light green.
- 3Read the lusterHold the specimen under a strong light. Luster: dull, glistening.
- 4Match the color rangeCompare against the expected color range: green, blue green, yellow green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: micaceous.
Often confused with
Glauconite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Glauconite leaves light green, Celadonite leaves greenish white.
How to tell apart: Streak differs, so Glauconite leaves light green, Chlorite leaves white; luster reads dull, glistening on Glauconite and pearly on Chlorite.
Often found alongside glauconite
Minerals reported to co-occur with glauconite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (K,Na)(Fe³⁺,Al,Mg)₂(Si,Al)₄O₁₀(OH)₂
- Mohs hardness
- 2
- Density
- 2.4-2.95 g/cm³
- Streak
- Light green
- Luster
- Dull, glistening
- Transparency
- Translucent to nearly opaque
- Crystal system
- Monoclinic
- Crystal habit
- Micaceous
- Cleavage
- {001}, perfect
- Rarity
- Common
- Uses
- Geological indicator, Soil additive
- Host rock
- Altered from detrital biotite or other parent materials, by marine diagenesis in shallow water under reducing conditions; especially in loosely consolidated sandstone (greensand), and impure limestone and siltstone
Where rockhounds find glauconite
2 mapped spotsClassic worldwide localities
- Particularly widespread, Alabama, USA
- Burnet Co., Texas, USA
- Both on and offshore in several of the coastal counties, California, USA
- Baker Co., Oregon, USA
- Otago Peninsula, New Zealand
- Flinders Ranges and Yorke Peninsula, South Australia
Field-hunting tip
Where it forms: Altered from detrital biotite or other parent materials, by marine diagenesis in shallow water under reducing conditions; especially in loosely consolidated sandstone (greensand), and impure limestone and siltstone. If you start seeing quartz, feldspars, glaucophane in float, you are in the right ground. Typical habit: micaceous. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Missouri, Utah. Start trip planning there.
Common questions
How do you identify glauconite?+
Where is glauconite found?+
Can I find glauconite in the United States?+
What rocks look like glauconite?+
What minerals are found with glauconite?+
What kind of rock does glauconite form in?+
What is glauconite used for?+
Find glauconite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
