Lime, specifically quicklime or calcium oxide, is an industrially processed product derived primarily from heating limestone. It is rarely found as a naturally occurring mineral due to its high reactivity with water and carbon dioxide in the atmosphere. Collectors primarily interact with it in historical industrial contexts or as processed chemical samples.

Hardness

3.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Semitransparent

mineralcommon

Lime

Hardness: 3.5
Luster: Vitreous
Streak: White
Transparency: Semitransparent

Is this lime?

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 lime with a known reference. Lime sits at Mohs 3.5, 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: white.
5
Look at form & habit
Crystal system: cubic. Typical habit: massive.

Often confused with

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

sedimentary

Limestone

Mohs 3

How to tell apart: Luster reads vitreous on Lime and dull to earthy on Limestone.

How to tell apart: Lime is noticeably harder (Mohs 3.5 vs. 1); luster reads vitreous on Lime and dull on Chalk.

Compare →

Often found alongside lime

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

All properties

Chemical formula: CaO
Mohs hardness: 3.5
Density: 3.345 g/cm³
Colors: White
Streak: White
Luster: Vitreous
Transparency: Semitransparent
Crystal system: Cubic
Crystal habit: Massive
Cleavage: {001}, perfect; parting on {011} (synthetic)
Rarity: Common
Uses: Industrial, Construction, Agricultural
Host rock: In thermally metamorphosed calcareous ejecta (Vesuvius, Italy); in burning coal measures (Kopeysk, Russia)

Where rockhounds find lime

Classic worldwide localities

Campbell mine, Bisbee, Cochise Co., Arizona, USA
Vesuvius, Campania, Italy
Kopeysk, Chelyabinsk coal basin, Southern Ural Mountains, Russia
Northern Siwaqa complex, Tulul Al Hammam area, Dead Sea region, Central Jordan

Field-hunting tip

Where it forms: In thermally metamorphosed calcareous ejecta (Vesuvius, Italy); in burning coal measures (Kopeysk, Russia). If you start seeing calcite, fluorellestadite, periclase in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop.

More lime photos

Common questions

How do you identify lime?+

Mohs hardness is 3.5. Luster: vitreous. The streak is white. Common colors include white.

Where is lime found?+

Notable localities include Campbell mine, Bisbee, Cochise Co., Arizona, USA; Vesuvius, Campania, Italy; Kopeysk, Chelyabinsk coal basin, Southern Ural Mountains, Russia; Northern Siwaqa complex, Tulul Al Hammam area, Dead Sea region, Central Jordan.

What rocks look like lime?+

Lime is most often confused with Limestone, Chalk. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with lime?+

Lime commonly co-occurs with Calcite, Fluorellestadite, Periclase, Magnesioferrite, Hematite, Srebrodolskite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does lime form in?+

Where it forms: In thermally metamorphosed calcareous ejecta (Vesuvius, Italy); in burning coal measures (Kopeysk, Russia). Working float back to the host body is the standard way to chase a fresh occurrence.

What is lime used for?+

Lime is used in industrial, construction, agricultural.

Find lime on the map

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