The Rock Cycle

The last chapter sorted rocks into three families. This chapter connects them. Igneous, sedimentary, and metamorphic rocks are not really three separate things. They are three stages the same material passes through, over and over, on a loop geologists call the rock cycle. The atoms in the granite of a mountain today may have been sea-floor mud a hundred million years ago, and lava before that. They are not done moving.

The most important idea here is also the one students most often get backward. The rock cycle has no starting point and no fixed order. It is not a checklist that runs igneous, then sedimentary, then metamorphic. It is a set of possible changes. Any rock can become any other rock, and some paths skip stages entirely. What decides the path is where the rock ends up and which process reaches it there.

Two things never change across the whole cycle. Matter is conserved, so nothing is created or destroyed, only rearranged. And energy keeps it turning, from two sources we will meet in a moment. Everything else, the specific rock, the specific path, is up for grabs.

The arrows in the rock cycle are processes, and there are only a handful worth knowing. Each one takes a material and turns it into the next.

Melting turns any rock into magma once it gets deep and hot enough. Cooling and crystallization turns magma into igneous rock, quickly at the surface or slowly underground. Weathering and erosion break any exposed rock into sediment and carry the pieces away. Compaction and cementation, together called lithification, press and glue that sediment into sedimentary rock. Heat and pressure change any buried rock into metamorphic rock without melting it. One more process matters. Uplift is the slow raising of deep rock back to the surface. It exposes buried rock to weathering, and it keeps the loop from being a one-way trip down.

Notice how each product points to a family. Cool magma and you get igneous. Lithify sediment and you get sedimentary. Cook a rock and you get metamorphic. The family name is really just a record of the last process that acted on the rock.

A cycle needs energy, and the rock cycle gets it from two sources working from opposite directions. From below comes Earth's internal heat, most of it from the slow radioactive decay of elements deep inside the planet. That heat powers everything that happens at depth. It melts rock into magma, drives the metamorphism that changes buried rock, and fuels the plate motion and uplift that push rock back toward the surface. From above come the sun and gravity, which power everything that happens at the surface. The sun drives the weather that breaks rock apart, and gravity pulls the loosened pieces downhill through erosion and lays them down as sediment.

This split is worth memorizing because the Regents exam asks it directly. Melting, metamorphism, and uplift come from inside the Earth. Weathering, erosion, and deposition come from the sun and gravity. The two sources hand rock back and forth. Surface processes break rock down and bury it, internal processes heat it and lift it back up, and the loop continues.

The best way to feel how the cycle works is to travel it. You start as a rock somewhere on the map below. Each step, you choose a process that could reach you where you are, and it transforms you into the next material. There is no goal and no wrong turn, only the loop. Watch how quickly you can revisit the same family by a different road.

If that path surprised you, that is the point. Most textbooks draw the rock cycle as a ring, and students come away thinking rock has to go around the outside in order, from magma to igneous to sediment to sedimentary to metamorphic and back. Real rock takes shortcuts across the middle all the time.

An igneous rock does not have to become sediment first. Bury it and it goes straight to metamorphic. Melt it and it is magma again. A sedimentary rock can skip metamorphism entirely and melt. A metamorphic rock exposed by uplift weathers straight back into sediment without ever melting. There is only one hard rule in the whole cycle. To become igneous, a material must pass through magma and then cool. Everything else is open. When the exam asks whether a rock must pass through every stage in a set order, the answer is always no.

One lap of the rock cycle is extremely slow. A granite forming deep in a mountain range might wait a hundred million years before uplift and weathering even expose it. The sediment it becomes might sit buried for another hundred million years before it is heated or melted. The cycle you just clicked through in ten seconds usually takes tens to hundreds of millions of years per step.

That pace is also what makes the rock cycle useful for measuring time. The processes are so slow and so steady that the rocks they produce record enormous spans of time. That is the whole basis of geologic history, which is the subject of a later unit. It is also why the cycle can have run continuously for four billion years and still be nowhere near finished.

The three New York rocks from the last chapter are really three moments in one cycle. The Adirondack gneiss began as ordinary sediment and rock more than a billion years ago. It was buried and changed into metamorphic rock deep inside a mountain range that has since eroded away completely. Those eroded pieces became sediment that helped build the flat sedimentary layers of the Catskills and western New York. The dark igneous rock of the Palisades cooled from magma that pushed up through those same sedimentary layers as Pangaea tore apart.

Stand anywhere in the state and you are standing on rock partway through the loop. Some of it is rising and weathering, and some of it is buried and waiting. Given enough time, the Adirondacks will erode into the sediment of some future coastline, and that sediment will become rock of its own.

• Rock Cycle Infographic (page 15). The official diagram, at the bottom of the same page as the igneous chart. Trace the arrows and label each with a process. Confirm for yourself that every rock type has a path to every other.
• Mineral Composition of Igneous Rocks and Bowen’s Reaction Series (page 14). The cooling half of the cycle, in detail.
• Schemes for Sedimentary and Metamorphic Rock Identification (page 7). The weathering, lithification, and heat-and-pressure halves.
• Radioactive Decay Data (page 1). The source of the internal heat that drives melting, metamorphism, and uplift.

Download the current tables from NYSED (2026 Revised Edition, used from the 2026-27 school year): Reference Tables for Earth and Space Sciences.

• The rock cycle has no beginning and no fixed order. Any rock can become any other rock.
• The processes are melting, cooling and crystallization, weathering and erosion, compaction and cementation, heat and pressure, and uplift. Each product names a rock family.
• Two energy sources drive the cycle: Earth's internal heat, from radioactive decay, powers melting, metamorphism, and uplift; the sun and gravity power weathering, erosion, and deposition.
• To become igneous, a material must melt and then cool. That is the one required path; everything else can be reached directly.
• Matter is conserved throughout, and one lap takes tens to hundreds of millions of years.
• New York's igneous, sedimentary, and metamorphic rocks are three stages of one ongoing cycle.

Ten Regents-style questions, one at a time in a focused view, each with an instant explanation. The set reshuffles when you reach the end, so you can keep practicing as long as you like.