Filamentous actin is polar and, therefore, the two ends of the filament are different. Because of this polarity, the filaments often fit into other cellular structures in only one orientation, in a similar manner to how many of the parts of man-made structures are assembled. Growth, the addition of monomeric actin to the filament, occurs predominantly in one direction; the plus direction.
Larger landscaping rocks, such as boulders, can cost upwards of $800 per ton. For example, a volcanic rock can cost $600 per ton, and an Artic white boulder can cost $150 per ton. Natural stone edging, ideal for gardens and walkways, can cost $200 to $600 per ton.
Danny Davis, owner of Davis Outdoor Maintenance, in Chattanooga, Tennessee, says the cost of crushed stone in his area is $100 to $120 per ton, installed. He says the average sized driveway is about 20-by-20 feet, which requires about 13 tons of crushed rock and costs $1,300 to $1,500, including materials and labor. Schott estimates the average cost for him to install a gravel driveway is $1,200 to $1,500. According to CostHelper, the prices range drastically, from as low as $300 to thousands of dollars. A 12-by-25-foot driveway, with at least 4 inches of gravel, can cost about $300 to $1,000. Professionals recommend having anywhere from 4 to 8 inches of gravel.