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.
Natural rock steps can cost $80 to $200 each. Faux landscaping rocks can cost $45 to $100 or more for a single rock that stands one to two feet high. A small bag of rocks, such as lava rocks or pea gravel, will cost $2 to $5 for a bag that covers 0.5 cubic feet.