False: Gravel does not have the lowest water holding capacity among all types of rock particles.

Explanation:
Gravel is a type of rock particle characterized by its rounded shape and size ranging from 2mm to 75mm. While it is true that gravel has relatively low water holding capacity compared to finer particles such as silt or clay, it does not have the lowest water holding capacity among all types of rock particles. Let's explore further to understand this more comprehensively.

Types of Rock Particles:
1. Gravel: Rounded rock particles with a size range of 2mm to 75mm.
2. Sand: Granular rock particles ranging in size from 0.06mm to 2mm.
3. Silt: Fine rock particles with a size range of 0.002mm to 0.06mm.
4. Clay: The finest rock particles with a size less than 0.002mm.

Water Holding Capacity:
The water holding capacity of rock particles depends on their size, shape, and porosity. Porosity refers to the amount of empty space within a material, which determines its ability to hold water. The larger the pore spaces, the higher the water holding capacity.

Comparison:
1. Gravel: Gravel particles have relatively large pore spaces due to their larger size and rounded shape. This allows water to pass through easily, resulting in low water holding capacity compared to finer particles like silt or clay.
2. Sand: Sand particles are smaller than gravel but still have reasonably large pore spaces. Therefore, sand has a higher water holding capacity than gravel but lower than silt or clay.
3. Silt: Silt particles are much smaller than gravel or sand. They have smaller pore spaces, which enables them to hold more water than gravel or sand particles.
4. Clay: Clay particles are the finest and have the smallest pore spaces. This gives them the highest water holding capacity among all types of rock particles.

Conclusion:
In conclusion, gravel does not have the lowest water holding capacity among all types of rock particles. Clay, with its fine particles and small pore spaces, has the highest water holding capacity, followed by silt, sand, and then gravel. It is important to consider the water holding capacity of different rock particles when studying water movement and soil properties.