Home » Tumbled Basalt Rocks (20-40mm)
Tumbled black basalt rocks, 20-40mm size, natural stone decor from Rock and Soil with smooth, rounded surfaces.
Tumbled basalt rocks, 20-40mm size, from Rock and Soil, showing smooth, dark gray volcanic stones for landscaping or decor.
Tumbled black basalt rocks, 20-40mm size, natural stone decor from Rock and Soil with smooth, rounded surfaces.
Tumbled basalt rocks, 20-40mm size, from Rock and Soil, showing smooth, dark gray volcanic stones for landscaping or decor.

Tumbled Basalt Rocks (20-40mm)

In stock - 4 items available
SKU: RTB40
$620.00 inc. GST

Cubic Metre Calculator

Need to calculate how much you’ll need? Use our cubic metre calculator below.

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Volume
For ordering ¼㎥, ⅓㎥ and ½㎥ quantities please call the office on (07) 3245 5677
Please note that deliveries to postcode 4178 (Fishermans Island) may incur additional toll fees.
Bulk Order Delivery: Large quantities or multiple bulk products may incur additional delivery charges. We'll contact you before applying any extra charges.
Frequently Asked Questions

Our 20–40mm Tumbled Basalt Rocks are dark grey natural stones that have been mechanically tumbled to create a smooth finish. They are a popular choice for contemporary landscape designs and are softer underfoot than crushed stone, making them a comfortable option for areas with foot traffic. These stones are commonly used for:

  • Decorative garden beds
  • Modern landscape designs
  • Pathways and feature areas
  • Around trees and shrubs
  • Water features and ponds
  • Pots and planter boxes

Our tumbled basalt has been mechanically tumbled to produce smooth, rounded edges, while crushed basalt has angular edges that compact more firmly and is more commonly used for pathways and driveways.

Tumbled basalt is the more premium choice if you're looking for a stone with a smoother, more refined appearance that is also more comfortable to walk on. Crushed basalt has sharper edges, making it better suited to applications where there is little foot traffic or where a compacted surface is required, such as pathways and driveways.

To calculate how much 20–40mm Tumbled Basalt Rocks you need for your project, measure the length and width of the area where the stones will be placed.

Next, determine the desired depth of the stones. The required depth will vary depending on your project and the area you need to cover.

Once you have your length, width, and depth measurements, you can use our cubic metre calculator above or calculate the volume manually using the following formula:
Volume = Length × Width × Depth

Recommended Depth: As a general guide, we recommend laying decorative stones at a depth of 40–50mm. However, the ideal depth will depend on your project and the size of the stones. Larger stones may require a deeper layer for even coverage, while smaller stones can often be laid slightly thinner.

Yes. We recommend installing weed mat underneath your 20–40mm Tumbled Basalt Rocks for several reasons.

Firstly, because the stones are a consistent dark colour, any green weeds that emerge will be highly visible. Secondly, the larger 20–40mm stones naturally create wider gaps, giving weeds more opportunity to grow through the surface. Installing weed mat also makes long-term garden maintenance much easier, helping keep your landscape looking neat while reducing the time spent weeding.

Our Tumbled Basalt 20-40mm pebbles are a bold, natural stone with a deep charcoal-grey tone and a smooth, semi-rounded finish. Sourced locally and tumbled for comfort underfoot, this larger-format basalt is ideal for feature garden beds, pathways, pots and areas where you want contrast against lighter landscaping materials. Often chosen by customers searching for black rocks or black pebbles, tumbled basalt delivers a strong, dark aesthetic while retaining the natural variation and texture of real stone.

Tumbled Basalt Benefits:

  • Ideal for garden beds, pathways, pots and feature landscaping

  • Larger 20-40mm size creates a strong visual impact

  • Tumbled for smoother edges and a more refined finish

  • Durable, high-quality basalt sourced from a local quarry

  • Works beautifully alongside lighter stones for contrast

Specifications:

  • Size: 20-40mm

  • Sold in increments of 1/4m³, 1/3m³, 1/2m³ and 1m³

  • Delivered

Looking for a true black stone?

If you’re searching for black rocks or black pebbles, it’s important to note that natural stone quarried from the earth cannot achieve a perfect jet-black colour — even the darkest basalt will present as deep grey or charcoal. For projects that require a richer, darker black appearance, our Kashmiri Black polished pebble range may better suit your vision. These are cut and polished stones (rather than naturally tumbled) and are available in small bags for feature areas.

Note: Rock colours appear darker when wet. For an accurate shade, view them dry or ask our staff for dry samples or photos of the product when dry. If you receive a delivery when it is or has been raining, wait at least 24 hours of dry weather to view the true colour of your stones.

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