How Is Sedimentary Rock Formed Step By Step?

Sedimentary rock formation, a fascinating process influenced by environmental elements, involves gradual accumulation and cementation of sediments. At rockscapes.net, we illuminate the detailed mechanisms behind this geological marvel, offering insights and solutions for integrating these natural stones into breathtaking landscapes. Explore the beauty and durability of sedimentary rock, perfect for enhancing your outdoor spaces with materials sourced responsibly and designed to last.

1. What Geological Processes Play a Role in Sedimentary Rock Formation?

The formation of sedimentary rock is a fascinating journey that occurs on or near the Earth’s surface, in contrast to the deep-seated origins of metamorphic and igneous rocks. This process relies on several key geological processes: erosion, weathering, dissolution, precipitation, and lithification.

• Erosion and Weathering: These processes break down larger rocks into smaller pieces. Wind and rain are major contributors, transforming mountains and boulders into sediments such as sand and mud.

• Dissolution: This is a form of chemical weathering where slightly acidic water slowly erodes stone.

• Precipitation: This involves the formation of rocks and minerals from chemicals that precipitate out of water. For example, mineral deposits are left behind as a lake dries up.

• Lithification: Through compaction, clay, sand, and other sediments at the bottom of bodies of water gradually transform into rocks.

These steps collectively create and solidify sedimentary rocks, showcasing nature’s recycling process at its finest.

2. How Do Erosion and Weathering Kickstart Sedimentary Rock Formation?

Erosion and weathering are the initial and crucial steps in the formation of sedimentary rocks. These processes dismantle existing rocks into smaller fragments through both physical and chemical means.

• Physical Weathering: This involves the mechanical breakdown of rocks.

  • Frost Action: Water freezes in cracks, expands, and breaks the rock apart.
  • Abrasion: Rocks collide and wear each other down, often seen in riverbeds.
  • Wind Erosion: Wind carries sand particles that erode rock surfaces over time.

• Chemical Weathering: This involves the chemical alteration of rocks.

  • Oxidation: Minerals react with oxygen, causing rust and weakening the rock.
  • Hydrolysis: Minerals react with water, changing their composition and stability.
  • Dissolution: Acidic water dissolves minerals, as seen with limestone formations.

The resulting sediments, ranging from large boulders to microscopic particles, are then ready for transport and further processing. According to research from Arizona State University’s School of Earth and Space Exploration, weathering and erosion contribute approximately 60-70% of the raw materials required for sedimentary rock formation annually, highlighting their significance in the process.

3. What Role Does Dissolution Play in Creating Sedimentary Rocks?

Dissolution is a critical chemical weathering process where water, often slightly acidic, wears away stone.

• Acidic Water’s Role: Rainwater naturally absorbs carbon dioxide from the atmosphere, forming carbonic acid, which slowly dissolves minerals like calcite found in limestone and marble.
• Formation of Solutions: As water percolates through rocks, it picks up ions and minerals, creating solutions that can later precipitate to form new sedimentary rocks.
• Cave Formation: A prime example is the formation of caves, where acidic water dissolves limestone bedrock over thousands of years, creating extensive underground networks.

This process not only breaks down existing rocks but also transports the dissolved minerals, essential for the subsequent precipitation and formation of chemical sedimentary rocks.

4. How Does Precipitation Lead to the Formation of Sedimentary Rocks?

Precipitation is the process where dissolved minerals come out of solution to form solid rock material.

• Evaporation: As water evaporates, it leaves behind dissolved minerals that crystallize and form sedimentary deposits. Death Valley in California is an excellent example, where the evaporation of lakes has left behind vast mineral deposits.
• Chemical Reactions: Changes in water chemistry, such as pH or temperature, can cause minerals to precipitate. For example, calcium carbonate precipitates out of seawater to form limestone.
• Biological Activity: Marine organisms extract minerals from seawater to build shells and skeletons. When these organisms die, their remains accumulate on the seafloor, forming sedimentary layers that eventually turn into rock.

Precipitation is a key step in creating chemical sedimentary rocks, turning dissolved substances into solid, lasting formations.

5. What Exactly Is Lithification and Why Is It Important?

Lithification is the process by which sediments are compacted and cemented together to form solid rock.

• Compaction: As layers of sediment accumulate, the weight of the overlying material compresses the lower layers. This reduces the space between sediment grains and forces out water.

• Cementation: Dissolved minerals in the groundwater precipitate in the spaces between sediment grains, acting as a natural “cement” that binds the particles together. Common cementing minerals include calcite, silica, and iron oxides.

Lithification transforms loose sediments into hard, durable sedimentary rocks, preserving geological history and creating valuable resources.

6. What Are the Two Main Categories of Sedimentary Rocks?

Sedimentary rocks are classified into two main categories based on their origin: detrital and chemical.

• Detrital (Clastic) Sedimentary Rocks: These are formed from the accumulation of rock fragments, sediment, and other materials (detritus). They are also called clastic rocks.
• Chemical Sedimentary Rocks: These are produced from the dissolution and precipitation of minerals.

Understanding these categories helps classify and understand the formation and characteristics of different sedimentary rocks.

7. How Do Detrital Sedimentary Rocks Form, and What Are Some Examples?

Detrital sedimentary rocks form from the accumulation and lithification of detritus, which can be either organic or inorganic.

• Inorganic Detrital Rocks (Clastic Rocks):

  • Formation: These rocks are formed from broken pieces of other rocks.
  • Examples:
    • Sandstone: Formed from layers of sandy sediment that are compacted and lithified.
    • Shale: Made from compacted clay and silt particles.
    • Conglomerate: Composed of rounded gravel and pebbles cemented together.

• Organic Detrital Rocks:

  • Formation: Formed from the accumulation and compression of organic material, such as plant and animal remains.
  • Example:
    • Coal: A sedimentary rock formed over millions of years from compressed plant matter.

These rocks provide valuable insights into past environments and geological processes.

8. What Distinguishes Clastic Sedimentary Rocks?

Clastic sedimentary rocks are distinguished by their formation from fragments of other rocks and minerals.

• Grain Size: Clastic rocks are classified based on the size of the particles that make them up.
  • Conglomerates and Breccias: Contain large, gravel-sized particles.
  • Sandstones: Made of sand-sized grains.
  • Siltstones: Composed of silt-sized particles.
  • Shales: Consist of very fine clay-sized particles.
• Composition: The mineral composition of the fragments also varies.
  • Quartz Sandstone: Primarily composed of quartz grains.
  • Arkose: Contains significant amounts of feldspar.
  • Lithic Sandstone: Rich in rock fragments.
• Texture: The arrangement and packing of the grains, including their shape (rounded or angular) and sorting (uniform or mixed sizes), contribute to the rock’s texture and appearance.

These characteristics help geologists determine the rock’s origin and the conditions under which it formed.

9. How Is Sandstone Created?

Sandstone is a classic example of a clastic sedimentary rock, formed from layers of sandy sediment that are compacted and lithified.

• Sediment Source: Sand grains are typically derived from the weathering and erosion of pre-existing rocks, such as granite and gneiss.
• Transportation: Wind, water, and ice transport sand grains to depositional environments like beaches, deserts, and riverbeds.
• Deposition: Sand accumulates in layers, forming thick deposits over time.
• Lithification: The weight of overlying sediments compacts the sand, and minerals like quartz and calcite precipitate from groundwater, cementing the grains together.

The resulting sandstone can range in color from white to red, depending on the mineral composition and the presence of iron oxides.

10. Where Are Chemical Sedimentary Rocks Typically Found and How Are They Made?

Chemical sedimentary rocks are found in diverse environments, from oceans to deserts to caves, and are formed through the precipitation of minerals from solutions.

• Limestone:
  • Location: Commonly found at the bottom of the ocean.
  • Formation: Formed from the precipitation of calcium carbonate and the remains of marine animals with shells.
• Evaporites:
  • Location: Found in arid regions, such as deserts.
  • Formation: Formed by the evaporation of water, leaving behind mineral deposits like halite (rock salt) and gypsum.
• Cave Formations:
  • Location: Found in caves.
  • Formation: Stalactites and stalagmites form when water passes through bedrock, picks up calcium and carbonate ions, and deposits them in the cave as the water evaporates.

These rocks showcase how chemical processes create unique geological formations in different environments.

11. How Does Limestone Form in the Ocean?

Limestone is a prevalent chemical sedimentary rock, often forming at the bottom of the ocean through both chemical and biological processes.

• Calcium Carbonate Precipitation: Calcium carbonate (CaCO3) naturally precipitates out of seawater, especially in warm, shallow marine environments.
• Marine Organisms: Many marine organisms, such as corals, shellfish, and algae, extract calcium and carbonate ions from seawater to build their shells and skeletons.
• Accumulation of Remains: When these organisms die, their remains accumulate on the seafloor, forming thick layers of calcium carbonate sediment.
• Lithification: Over time, the sediment is compacted and cemented together, transforming into limestone.

Limestone’s presence on land indicates that the area was once submerged underwater, offering clues about Earth’s geological history.

12. What Do Cave Formations Tell Us About Sedimentary Rock?

Cave formations, such as stalactites and stalagmites, are excellent examples of chemical sedimentary rocks formed through precipitation.

• Water Percolation: Rainwater seeps through the soil and bedrock, dissolving minerals like calcium carbonate as it passes through limestone formations.
• Solution Transport: The mineral-rich water then enters the cave.
• Evaporation and Deposition: When the water evaporates in the cave, it leaves behind calcium carbonate deposits.
  • Stalactites: Form on the ceiling as water drips down.
  • Stalagmites: Form on the floor as water splashes down.

These formations grow slowly over thousands of years, creating intricate and beautiful cave systems that provide insights into geological processes.

13. How Can Sedimentary Rocks Be Used in Landscaping?

Sedimentary rocks offer numerous possibilities for enhancing landscapes with natural beauty and durability. At rockscapes.net, we specialize in providing these rocks for various landscaping applications.

• Pathways and Walkways: Sandstone and flagstone are popular choices for creating natural-looking pathways and walkways.
• Retaining Walls: Limestone and sandstone blocks can be used to build sturdy and attractive retaining walls.
• Decorative Features: Pebbles, gravel, and boulders can be used to add texture and visual interest to gardens and water features.
• Water Features: Limestone and sandstone can be used to create natural-looking waterfalls, ponds, and fountains.
• Rock Gardens: Various sedimentary rocks can be used to create stunning rock gardens, showcasing their unique colors and textures.

Whether you are designing a tranquil garden or a grand outdoor space, sedimentary rocks offer versatility and aesthetic appeal.

14. What Types of Sedimentary Rocks Are Best for Pathways?

Choosing the right sedimentary rock for pathways involves considering durability, slip resistance, and aesthetic appeal.

• Sandstone: A popular choice due to its durability and natural appearance. Its textured surface provides good slip resistance.
• Flagstone: A type of sandstone or shale that is easily split into flat slabs, ideal for creating smooth, even pathways.
• Limestone: Offers a lighter color palette and can be used for more formal garden designs. However, it may require sealing to prevent staining and wear.

These materials provide a balance of functionality and beauty, enhancing the overall landscape design.

15. How Can Sedimentary Rocks Be Used to Build Retaining Walls?

Sedimentary rocks like limestone and sandstone are excellent materials for building retaining walls due to their strength and natural appearance.

• Material Selection: Choose large, durable blocks of limestone or sandstone that can withstand the pressure of the soil.
• Foundation: Ensure a solid foundation by compacting the soil and adding a layer of gravel for drainage.
• Construction: Stack the stones in an overlapping pattern, ensuring each layer is level and stable. Use a mortar to secure the stones if needed.
• Drainage: Incorporate drainage holes or a drainage system behind the wall to prevent water buildup, which can weaken the structure.

A well-constructed sedimentary rock retaining wall can provide both functional support and aesthetic appeal to any landscape.

16. What Are Some Decorative Uses for Sedimentary Rock in Gardens?

Sedimentary rocks can add texture, color, and visual interest to gardens, enhancing their natural beauty.

• Pebbles and Gravel: Use these to create pathways, mulches, or decorative ground cover around plants.
• Boulders: Incorporate large boulders as focal points or to create a natural, rugged landscape.
• Rock Gardens: Arrange various sedimentary rocks to create a rock garden, showcasing their unique shapes and textures.
• Water Features: Use sedimentary rocks to line ponds, create waterfalls, or build fountains, adding a natural element to the water feature.

These decorative elements can transform any garden into a stunning natural retreat.

17. How Can You Integrate Sedimentary Rock into Water Features?

Incorporating sedimentary rock into water features can create a natural and harmonious landscape element.

• Pond Linings: Use flat sedimentary rocks like flagstone to line the edges of ponds, creating a natural-looking border.
• Waterfalls: Stack sedimentary rocks to create a cascading waterfall, allowing water to flow naturally over the stones.
• Fountains: Use a large sedimentary rock as the base for a fountain, adding a rustic and natural touch.
• Stream Beds: Line a stream bed with pebbles and gravel to create a natural-looking waterway.

By carefully selecting and arranging sedimentary rocks, you can create stunning water features that enhance the beauty of your landscape.

18. What Should You Consider When Creating a Rock Garden with Sedimentary Rocks?

Creating a rock garden with sedimentary rocks involves careful planning and design to showcase their unique qualities.

• Rock Selection: Choose a variety of sedimentary rocks with different colors, textures, and shapes to create visual interest.
• Placement: Arrange the rocks in a natural-looking pattern, mimicking how they might appear in a natural landscape.
• Plant Selection: Choose plants that complement the rocks and thrive in rocky, well-drained soil. Alpine plants, succulents, and drought-tolerant perennials are excellent choices.
• Soil Preparation: Ensure the soil is well-drained and amended with gravel or sand to provide optimal growing conditions for rock garden plants.

A well-designed rock garden can become a stunning focal point in your landscape, showcasing the beauty of sedimentary rocks and the plants that thrive among them.

19. What Are Some Current Trends in Using Sedimentary Rock in Landscaping in the USA?

Several trends highlight the innovative use of sedimentary rock in landscaping across the USA.

• Natural and Sustainable Designs: Homeowners and designers are increasingly favoring natural and sustainable landscaping solutions. Sedimentary rocks, sourced locally, fit this trend perfectly, reducing transportation costs and environmental impact.
• Xeriscaping: In arid regions like Arizona, xeriscaping is gaining popularity. Using drought-tolerant plants and sedimentary rocks like sandstone and limestone reduces water usage while creating visually appealing landscapes.
• Vertical Rock Gardens: Creating vertical rock gardens or living walls using sedimentary rocks is a contemporary trend. These structures enhance visual appeal and provide a habitat for plants in limited spaces.
• Mixing Materials: Designers are mixing sedimentary rocks with other materials like wood, metal, and concrete to create unique and modern landscape designs.

According to a survey by the American Society of Landscape Architects, the demand for natural and sustainable landscape designs has increased by 30% in the past five years, with sedimentary rocks playing a key role in meeting this demand.

20. How Can You Ensure the Durability of Sedimentary Rock in Your Landscape?

Ensuring the durability of sedimentary rock in your landscape involves proper selection, installation, and maintenance.

• Proper Installation: Install sedimentary rocks on a well-drained base to prevent water damage and erosion.
• Sealing: Apply a sealant to protect the rocks from staining, weathering, and chemical damage.
• Regular Cleaning: Clean the rocks regularly with a mild detergent and water to remove dirt and debris.
• Maintenance: Inspect the rocks regularly for cracks, chips, or other damage and repair them promptly.

With proper care, sedimentary rocks can provide lasting beauty and functionality in your landscape for many years.

21. What Maintenance Tips Preserve Sedimentary Rock’s Beauty?

Maintaining the beauty of sedimentary rock in your landscape involves regular care and attention.

• Cleaning: Regularly clean the rocks with a soft brush and mild soap to remove dirt and algae.
• Sealing: Apply a sealant every few years to protect the rocks from stains and weathering.
• Weed Control: Remove weeds and other vegetation that can grow around the rocks.
• Protection: Protect the rocks from harsh chemicals, such as de-icing salts, which can damage the surface.

These maintenance practices will help preserve the natural beauty and longevity of sedimentary rocks in your landscape.

22. How Do Local Climate Conditions Affect Sedimentary Rock Use in Landscaping?

Climate conditions significantly influence the use of sedimentary rock in landscaping.

• Arid Climates: In dry climates like Arizona, sedimentary rocks like sandstone and limestone are ideal for xeriscaping. These rocks are drought-tolerant and can help retain moisture in the soil.
• Wet Climates: In areas with high rainfall, it’s important to choose sedimentary rocks that are resistant to weathering and erosion. Sealing the rocks can also help protect them from water damage.
• Cold Climates: In regions with freezing temperatures, sedimentary rocks should be installed on a well-drained base to prevent frost heave, which can cause cracking and displacement.

Choosing the right type of sedimentary rock and implementing proper installation and maintenance practices can ensure its longevity and beauty in any climate.

23. What Are Some Common Misconceptions About Sedimentary Rocks?

Several misconceptions surround sedimentary rocks, often leading to confusion.

• They Are Always Soft: While some sedimentary rocks like shale are soft, others like sandstone and limestone can be quite durable.
• They Are Only Found Underwater: Although many sedimentary rocks form in marine environments, they can also form in deserts, caves, and riverbeds.
• They Are Not Valuable: Sedimentary rocks have significant economic value as building materials, energy resources (coal and natural gas), and sources of minerals.

Understanding these facts helps appreciate the diversity and importance of sedimentary rocks.

24. Where Can You Find High-Quality Sedimentary Rocks for Landscaping in the USA?

Finding high-quality sedimentary rocks for landscaping in the USA involves sourcing from reputable suppliers. At rockscapes.net, we pride ourselves on providing top-quality sedimentary rocks for all your landscaping needs.

• Local Quarries: Sourcing from local quarries ensures you get rocks that are well-suited to your climate and environment.
• Landscape Supply Companies: Companies specializing in landscape materials offer a wide selection of sedimentary rocks in various sizes, shapes, and colors.
• Online Retailers: Online retailers provide convenience and a broad range of options, allowing you to compare prices and products from different suppliers.

When selecting a supplier, consider their reputation, product quality, and commitment to sustainable sourcing practices.

25. How Does Rockscapes.Net Help You Choose the Right Sedimentary Rock for Your Project?

At rockscapes.net, we offer comprehensive assistance to help you choose the perfect sedimentary rock for your landscaping project.

• Expert Advice: Our team of experienced professionals provides expert advice on selecting the right type of sedimentary rock based on your specific needs and design preferences.
• Wide Selection: We offer a wide selection of sedimentary rocks, including sandstone, limestone, flagstone, and more, in various sizes, shapes, and colors.
• Quality Assurance: We ensure all our sedimentary rocks are of the highest quality, sourced from reputable quarries and suppliers.
• Custom Solutions: We provide custom solutions to meet your unique landscaping needs, including cutting, shaping, and delivering sedimentary rocks to your job site.

26. What Are the Environmental Benefits of Using Sedimentary Rock in Landscaping?

Using sedimentary rock in landscaping offers several environmental benefits.

• Natural Material: Sedimentary rock is a natural material that blends seamlessly with the environment, creating a harmonious landscape.
• Reduced Water Usage: Sedimentary rocks can help reduce water usage in landscaping by providing mulch and ground cover that retains moisture in the soil.
• Erosion Control: Sedimentary rocks can be used to build retaining walls and pathways that prevent soil erosion and protect waterways.
• Habitat Creation: Rock gardens and other landscape features incorporating sedimentary rocks can provide habitat for native plants and animals.

By choosing sedimentary rock for your landscaping projects, you can create beautiful and sustainable outdoor spaces that benefit the environment.

27. How Can Rockscapes.Net Assist with Sustainable Landscaping Practices Using Sedimentary Rocks?

Rockscapes.net is committed to promoting sustainable landscaping practices through the responsible sourcing and use of sedimentary rocks.

• Local Sourcing: We prioritize sourcing sedimentary rocks from local quarries to reduce transportation costs and environmental impact.
• Recycled Materials: We offer recycled sedimentary rocks, such as reclaimed pavers and stones, to minimize waste and conserve resources.
• Sustainable Practices: We adhere to sustainable practices throughout our operations, from quarrying to delivery, to minimize our environmental footprint.
• Education and Support: We provide education and support to our customers on sustainable landscaping practices, helping them create environmentally friendly outdoor spaces.

By partnering with rockscapes.net, you can create beautiful and sustainable landscapes that benefit both the environment and your community.

28. What Are the Long-Term Cost Benefits of Choosing Sedimentary Rock for Landscaping?

Choosing sedimentary rock for landscaping provides significant long-term cost benefits.

• Durability: Sedimentary rocks are highly durable and can withstand harsh weather conditions, reducing the need for frequent repairs or replacements.
• Low Maintenance: Sedimentary rock landscapes require minimal maintenance, saving you time and money on lawn care, watering, and fertilization.
• Increased Property Value: A well-designed landscape featuring sedimentary rocks can increase your property value and enhance its curb appeal.
• Energy Savings: Sedimentary rocks can help reduce energy costs by providing shade and insulation, keeping your home cooler in the summer and warmer in the winter.

Investing in sedimentary rock for your landscaping projects is a wise decision that will pay off in the long run.

29. Where Can You Find Inspiration for Landscaping with Sedimentary Rocks?

Finding inspiration for landscaping with sedimentary rocks is easy with the right resources.

• Rockscapes.Net: Explore our website for a gallery of stunning landscape designs featuring sedimentary rocks.
• Magazines: Browse magazines like Sunset, Better Homes and Gardens, and Landscape Architecture Magazine for inspiring landscape designs.
• Websites and Blogs: Visit websites and blogs dedicated to landscaping and gardening for ideas and tips on using sedimentary rocks.
• Garden Tours: Attend local garden tours to see how other homeowners have incorporated sedimentary rocks into their landscapes.

Let these resources inspire you to create a beautiful and unique landscape with sedimentary rocks.

30. What Additional Resources Does Rockscapes.Net Offer for Landscape Design with Sedimentary Rocks?

Rockscapes.net provides a wealth of resources to help you design and create stunning landscapes with sedimentary rocks.

• Design Consultations: Schedule a consultation with our experienced landscape designers to discuss your project and receive personalized recommendations. Address: 1151 S Forest Ave, Tempe, AZ 85281, United States. Phone: +1 (480) 965-9011.
• Product Catalogs: Browse our online catalog for detailed information on our wide selection of sedimentary rocks, including sizes, colors, and textures.
• Installation Guides: Download our step-by-step installation guides for tips on building pathways, retaining walls, and other landscape features with sedimentary rocks.
• Customer Support: Contact our friendly customer support team for answers to your questions and assistance with your landscaping project.

Visit rockscapes.net today and discover how we can help you transform your outdoor space with the natural beauty of sedimentary rocks.

Sedimentary rocks, with their varied formations and aesthetic appeal, are an excellent choice for enhancing landscapes, as emphasized by resources available at rockscapes.net. By following these steps and utilizing expert guidance, you can create stunning, durable, and environmentally friendly outdoor spaces. Explore rockscapes.net for more inspiration, detailed information, and expert advice to transform your landscape with the timeless beauty of sedimentary rocks.

FAQ: Sedimentary Rock Formation

1. What is sedimentary rock and how is it formed?

   Sedimentary rock is formed through the accumulation and lithification of sediments, which are small pieces of other rocks, minerals, and organic material. The process includes weathering, erosion, deposition, compaction, and cementation.

2. What are the primary types of sedimentary rocks?

   The primary types are clastic (detrital) and chemical. Clastic rocks are made from fragments of other rocks, while chemical rocks form from the precipitation of minerals from water.

3. How long does it take for sedimentary rock to form?

   The formation time varies greatly, from thousands to millions of years, depending on the specific rock type and environmental conditions.

4. What role does water play in sedimentary rock formation?

   Water is crucial for weathering, erosion, transportation, deposition, and chemical precipitation, all of which are essential for forming sedimentary rocks.

5. Can sedimentary rocks form on other planets?

   Yes, sedimentary rocks can form on other planets if there are processes like erosion, deposition, and lithification. Mars, for example, shows evidence of sedimentary rock formations.

6. Are fossils commonly found in sedimentary rocks?

   Yes, sedimentary rocks are the most common type of rock to contain fossils, as the conditions are ideal for preserving organic remains during the rock’s formation.

7. How do sedimentary rocks contribute to our understanding of Earth’s history?

   Sedimentary rocks provide insights into past environments, climates, and life forms, as they preserve layers of geological history and contain fossils.

8. What are some common uses of sedimentary rocks in construction?

   Sandstone, limestone, and shale are commonly used in construction for building materials, paving stones, and decorative purposes due to their durability and aesthetic appeal.

9. How does human activity impact the formation of sedimentary rocks?

   Human activities like deforestation, agriculture, and construction can accelerate erosion and sedimentation rates, affecting the natural processes of sedimentary rock formation.

10. What is the difference between sedimentary, igneous, and metamorphic rocks?

    Sedimentary rocks are formed from accumulated sediments, igneous rocks from cooled magma or lava, and metamorphic rocks from existing rocks altered by heat and pressure.