Mont. Code Ann. § 70-4-203

When a thing has been formed by the combination of several materials of different owners and none of the materials can be considered the principal substance, an owner without whose consent the combination was made may require a separation if the materials can be separated without inconvenience. If they cannot be separated, the owners acquire the thing in common, in proportion to the quantity, quality, and value of their materials, but if the materials of one were far superior to those of the others, both in quantity and value, the person may claim the thing on reimbursing to the others the value of their materials.