Learn · Module A
Rock Identification Lab
Look closely, ask the right questions and sort Oman’s rocks into their families — the way geologists do in the field.
The specimen collection
15 rocks, minerals and fossils from Oman’s story
2 are shown with real photographs — GeoAstro’s own or licensed specimens, credited in the Rock Explorer. The rest use a labelled Scientific illustration until a suitable photograph is approved.
- IgneousPeridotiteIllustration · photo needed
- IgneousDolerite (sheeted dykes)Illustration · photo needed
- SedimentaryLimestoneIllustration · photo needed
- FossilFossil coralIllustration · photo needed
- FossilStromatoliteIllustration · photo needed
- SedimentaryGlacial depositIllustration · photo needed
- MetamorphicEclogiteIllustration · photo needed
- MetamorphicMetamorphic rocks (schist)Illustration · photo needed
- SedimentaryTravertineIllustration · photo needed
- StructureSheath foldIllustration · photo needed
- MineralOlivineIllustration · photo needed
- MineralGarnetIllustration · photo needed
- MineralCalciteIllustration · photo needed
Identify a rock
Answer what you see — the key does the rest
Geologists identify rocks by looking closely: crystals or grains, layers, fossils and colour. Follow the questions as you would in the field.
Question 1
What do you notice first about the rock?
Look at the whole rock first, then up close with a hand lens.
Question 1
What kind of pattern can you see?
Question 1
Is it porous or banded, like a spring deposit?
Geologists test these rocks with a drop of dilute acid: calcite fizzes. Only your guide does this test.
Question 1
How are the crystals arranged?
Question 1
How big are the crystals?
Crystal size tells you how fast the magma cooled.
Your rock is probably
Fossil coral
Fossil
- Looks like
- Honeycomb or branching patterns preserved in limestone.
- How it forms
- Remains of corals that lived on the shallow sea floor.
- In Oman
- Fossil corals occur in Oman’s limestones.
Your rock is probably
Stromatolite
Fossil
- Looks like
- Fine wavy or domed layers in carbonate rock.
- How it forms
- Built layer by layer by microbial mats that trapped sediment.
- In Oman
- Occur in Oman’s Neoproterozoic carbonate rocks.
Your rock is probably
Limestone
Sedimentary
- Looks like
- Pale grey to cream rock, often containing fossils.
- How it forms
- Built up from calcium carbonate in warm, shallow seas.
- In Oman
- Thick Permian–Cretaceous limestones (Hajar Supergroup) form much of Jabal Akhdar; younger Tertiary limestones occur around Muscat.
Your rock is probably
Glacial deposit
Sedimentary
- Looks like
- Pebbles and boulders of mixed sizes in a fine-grained matrix.
- How it forms
- Debris carried and dropped by glaciers.
- In Oman
- Neoproterozoic (Cryogenian) glacial deposits are preserved in Oman, including diamictites of the Abu Mahara Group on the Saiq Plateau of Jabal Akhdar.
Your rock is probably
Metamorphic rocks (schist)
Metamorphic
- Looks like
- Rocks with a layered, often shiny foliation.
- How it forms
- Existing rocks changed by heat and pressure without melting.
- In Oman
- The Saih Hatat area near Muscat contains metamorphic rocks formed during Late Cretaceous subduction.
Your rock is probably
Eclogite
Metamorphic
- Looks like
- Green rock studded with red garnet crystals.
- How it forms
- Formed at very high pressure, deep in a subduction zone.
- In Oman
- High-pressure rocks of the Saih Hatat area, including As Sifah, formed in the Late Cretaceous (about 80 million years ago).
Your rock is probably
Gabbro
Igneous
- Looks like
- Coarse-grained, speckled dark and light crystals.
- How it forms
- Magma that cooled slowly deep in the oceanic crust.
- In Oman
- The lower crust of the Samail ophiolite; zircon in these gabbros is dated to about 96–95 million years ago.
Your rock is probably
Dolerite (sheeted dykes)
Igneous
- Looks like
- Medium-grained dark rock in parallel vertical sheets.
- How it forms
- Magma that filled cracks as the sea floor pulled apart, feeding the lavas above.
- In Oman
- The sheeted dyke complex of the Samail ophiolite.
Your rock is probably
Basalt & pillow lava
Igneous
- Looks like
- Fine-grained dark rock forming rounded, pillow-shaped bodies.
- How it forms
- Basalt lava erupted under the sea and chilled quickly into pillows.
- In Oman
- Pillow lavas form the upper part of the ophiolite sequence; pillow lavas are also a stop on our Jabal Akhdar route.
Your rock is probably
Peridotite
Igneous
- Looks like
- Dense, dark green rock that often weathers to a rusty brown surface.
- How it forms
- Formed in Earth’s upper mantle, below the oceanic crust.
- In Oman
- Forms the mantle section of the Samail ophiolite in the Oman Mountains.
Your rock is probably
Travertine
Sedimentary
- Looks like
- Pale, porous or banded carbonate rock.
- How it forms
- Carbonate minerals precipitated from spring water.
- In Oman
- Forms today where groundwater reacts with mantle peridotite; on the Saiq Plateau of Jabal Akhdar, older spring travertine was deposited where water emerged from limestone.
Still possible · 11
- Fossil coral
- Stromatolite
- Limestone
- Glacial deposit
- Metamorphic rocks (schist)
- Eclogite
- Dolerite (sheeted dykes)
- Peridotite
- Travertine
A real identification needs a hand lens, a fresh surface and simple tests — ask your GeoAstro guide in the field.
Look closely
Use the lens like a field geologist
Move the magnifier over each specimen — with your mouse, your finger or the arrow keys — then answer what you observe.
Challenge 1 of 6
Move the lens over the rock. Can you see separate crystals?
Gabbro cooled slowly deep in the crust, so its crystals had time to grow large.
Challenge 2 of 6
What colour are the round crystals scattered through the green rock?
The red crystals are garnet, a mineral that grows at high pressure.
Challenge 3 of 6
How are the mineral grains arranged?
Heat and pressure line the minerals up, giving a layered texture called foliation.
Challenge 4 of 6
Are the pebbles all the same size?
Glaciers carry and drop debris of every size together, so glacial deposits are poorly sorted.
Challenge 5 of 6
Look at the rock face the guide is pointing to. Which shapes tell you how this lava erupted?
Rounded pillows form when lava erupts under water and its surface chills instantly.
Challenge 6 of 6
Look closely at the cut surface. What does the pattern come from?
Honeycomb or branching patterns preserved in limestone are the remains of corals.
Classification activity
Sort the rocks into their families
Tap a specimen, then tap the family you think it belongs to. Think about how each rock formed.
Choose a specimen to begin.
Educational comparisons
Similar at first sight, different stories
Comparing rocks side by side is how geologists learn what each clue means.
Gabbro
Dolerite (sheeted dykes)
Basalt & pillow lava
Gabbro, dolerite and basalt can form from similar magma. What changes is how fast it cooled: slowly deep in the crust gives large crystals; quickly on the sea floor gives tiny ones.
Limestone
Travertine
Both are made mostly of calcite. Limestone built up in warm, shallow seas; travertine precipitates from spring water.
Metamorphic rocks (schist)
Eclogite
Both are metamorphic rocks. Schist shows minerals lined up in layers; eclogite formed at very high pressure, deep in a subduction zone, and contains red garnet.
Fossil coral
Stromatolite
Fossil corals are the remains of animals that lived on the shallow sea floor. Stromatolites were built layer by layer by microbial mats — among the oldest traces of life.
Compare any two specimens
Igneous
Peridotite
- Looks like
- Dense, dark green rock that often weathers to a rusty brown surface.
- How it forms
- Formed in Earth’s upper mantle, below the oceanic crust.
- Minerals
- Olivine, Pyroxene, Serpentine (alteration)
Igneous
Gabbro
- Looks like
- Coarse-grained, speckled dark and light crystals.
- How it forms
- Magma that cooled slowly deep in the oceanic crust.
- Minerals
- Plagioclase, Pyroxene
Igneous
Dolerite (sheeted dykes)
- Looks like
- Medium-grained dark rock in parallel vertical sheets.
- How it forms
- Magma that filled cracks as the sea floor pulled apart, feeding the lavas above.
Igneous
Basalt & pillow lava
- Looks like
- Fine-grained dark rock forming rounded, pillow-shaped bodies.
- How it forms
- Basalt lava erupted under the sea and chilled quickly into pillows.
Sedimentary
Limestone
- Looks like
- Pale grey to cream rock, often containing fossils.
- How it forms
- Built up from calcium carbonate in warm, shallow seas.
- Minerals
- Calcite
Fossil
Fossil coral
- Looks like
- Honeycomb or branching patterns preserved in limestone.
- How it forms
- Remains of corals that lived on the shallow sea floor.
Fossil
Stromatolite
- Looks like
- Fine wavy or domed layers in carbonate rock.
- How it forms
- Built layer by layer by microbial mats that trapped sediment.
Sedimentary
Glacial deposit
- Looks like
- Pebbles and boulders of mixed sizes in a fine-grained matrix.
- How it forms
- Debris carried and dropped by glaciers.
Metamorphic
Eclogite
- Looks like
- Green rock studded with red garnet crystals.
- How it forms
- Formed at very high pressure, deep in a subduction zone.
- Minerals
- Garnet, Omphacite
Metamorphic
Metamorphic rocks (schist)
- Looks like
- Rocks with a layered, often shiny foliation.
- How it forms
- Existing rocks changed by heat and pressure without melting.
Sedimentary
Travertine
- Looks like
- Pale, porous or banded carbonate rock.
- How it forms
- Carbonate minerals precipitated from spring water.
Structure
Sheath fold
- Looks like
- A tube- or cone-shaped fold in strongly deformed rock.
- How it forms
- Formed when rock is intensely sheared and stretched.
Mineral
Olivine
- Looks like
- Olive-green glassy grains.
- How it forms
- A main mineral of Earth’s upper mantle.
Mineral
Garnet
- Looks like
- Deep red, rounded crystals.
- How it forms
- Grows in rocks under high pressure and temperature.
Mineral
Calcite
- Looks like
- White to colourless mineral, the main component of limestone and travertine.
- How it forms
- Precipitates from sea water, spring water or living organisms.
Igneous
Peridotite
- Looks like
- Dense, dark green rock that often weathers to a rusty brown surface.
- How it forms
- Formed in Earth’s upper mantle, below the oceanic crust.
- Minerals
- Olivine, Pyroxene, Serpentine (alteration)
Igneous
Gabbro
- Looks like
- Coarse-grained, speckled dark and light crystals.
- How it forms
- Magma that cooled slowly deep in the oceanic crust.
- Minerals
- Plagioclase, Pyroxene
Igneous
Dolerite (sheeted dykes)
- Looks like
- Medium-grained dark rock in parallel vertical sheets.
- How it forms
- Magma that filled cracks as the sea floor pulled apart, feeding the lavas above.
Igneous
Basalt & pillow lava
- Looks like
- Fine-grained dark rock forming rounded, pillow-shaped bodies.
- How it forms
- Basalt lava erupted under the sea and chilled quickly into pillows.
Sedimentary
Limestone
- Looks like
- Pale grey to cream rock, often containing fossils.
- How it forms
- Built up from calcium carbonate in warm, shallow seas.
- Minerals
- Calcite
Fossil
Fossil coral
- Looks like
- Honeycomb or branching patterns preserved in limestone.
- How it forms
- Remains of corals that lived on the shallow sea floor.
Fossil
Stromatolite
- Looks like
- Fine wavy or domed layers in carbonate rock.
- How it forms
- Built layer by layer by microbial mats that trapped sediment.
Sedimentary
Glacial deposit
- Looks like
- Pebbles and boulders of mixed sizes in a fine-grained matrix.
- How it forms
- Debris carried and dropped by glaciers.
Metamorphic
Eclogite
- Looks like
- Green rock studded with red garnet crystals.
- How it forms
- Formed at very high pressure, deep in a subduction zone.
- Minerals
- Garnet, Omphacite
Metamorphic
Metamorphic rocks (schist)
- Looks like
- Rocks with a layered, often shiny foliation.
- How it forms
- Existing rocks changed by heat and pressure without melting.
Sedimentary
Travertine
- Looks like
- Pale, porous or banded carbonate rock.
- How it forms
- Carbonate minerals precipitated from spring water.
Structure
Sheath fold
- Looks like
- A tube- or cone-shaped fold in strongly deformed rock.
- How it forms
- Formed when rock is intensely sheared and stretched.
Mineral
Olivine
- Looks like
- Olive-green glassy grains.
- How it forms
- A main mineral of Earth’s upper mantle.
Mineral
Garnet
- Looks like
- Deep red, rounded crystals.
- How it forms
- Grows in rocks under high pressure and temperature.
Mineral
Calcite
- Looks like
- White to colourless mineral, the main component of limestone and travertine.
- How it forms
- Precipitates from sea water, spring water or living organisms.
Learn in the field
Take the lesson outdoors with GeoAstro Oman
School geology program
Classroom preparation, a guided field trip and follow-up activities for your students.
Book School Geology Programbooking enquiry via WhatsApp (opens WhatsApp in a new tab)Muscat Geology Tour
Seven stops from the ophiolite to the Sifah eclogite.
Book Muscat Geology Tourbooking enquiry via WhatsApp (opens WhatsApp in a new tab)Jabal Akhdar Geology Tour
Five stops from Coral Park to the cultural hike in Al Ain village.
Book Jabal Akhdar Geology Tourbooking enquiry via WhatsApp (opens WhatsApp in a new tab)University field experience
Field description, structures and the published literature, in Oman’s mountains.
Request University Field Experiencebooking enquiry via WhatsApp (opens WhatsApp in a new tab)
A WhatsApp message is an enquiry, not a confirmed booking. Our team will reply to confirm availability, details and the programme. Experiences depend on sky and weather conditions.