| PROPERTY, PLANT, EQUIPMENT AND MINERAL PROPERTIES |
PROPERTY, PLANT, EQUIPMENT, AND MINERAL PROPERTIES "Property, plant, equipment, and mineral properties, net" were comprised of the following (in thousands): | | | | | | | | | | | | December 31, | | | 2018 | | 2017 | Buildings and plant | | $ | 81,429 |
| | $ | 79,757 |
| Machinery and equipment | | 241,977 |
| | 234,861 |
| Vehicles | | 5,669 |
| | 4,835 |
| Office equipment and improvements | | 13,779 |
| | 12,637 |
| Ponds and land improvements | | 58,961 |
| | 56,194 |
| Total depreciable assets | | 401,815 |
| | 388,284 |
| Accumulated depreciation | | $ | (167,168 | ) | | $ | (141,818 | ) | Total depreciable assets, net | | $ | 234,647 |
| | $ | 246,466 |
| | | | | | Mineral properties and development costs | | 139,418 |
| | 138,841 |
| Accumulated depletion | | (31,197 | ) | | (26,840 | ) | Total depletable assets, net | | 108,221 |
| | 112,001 |
| | | | | | Land | | $ | 519 |
| | $ | 519 |
| Construction in progress | | 2,822 |
| | 5,556 |
| Total property, plant, equipment, and mineral properties, net | | $ | 346,209 |
| | $ | 364,542 |
|
We incurred the following expenses for depreciation and depletion, including expenses capitalized into inventory, for the following periods (in thousands): | | | | | | | | | | | | | | | | Year Ended December 31, | | | 2018 | | 2017 | | 2016 | Depreciation | | $ | 27,858 |
| | $ | 28,323 |
| | $ | 36,169 |
| Depletion | | 4,357 |
| | 4,886 |
| | 4,744 |
| Total incurred | | $ | 32,215 |
| | $ | 33,209 |
| | $ | 40,913 |
|
|