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Property, Plant and Equipment, net
 12 Months Ended
Dec. 31, 2018
Property, Plant and Equipment [Abstract]  
Property, Plant and Equipment, net
Property, Plant and Equipment, net
Net property, plant and equipment consists of:
 
December 31,
 
2018
 
2017
Machinery, equipment and tooling
$
14,858

 
$
7,802

Wellsite proppant storage solutions
5,286

 
—

Vehicles
1,955

 
1,546

Furniture and fixtures
1,140

 
720

Plant and building
158,882

 
81,561

Real estate properties
4,601

 
4,432

Railroad and sidings
27,347

 
10,254

Land and land improvements
27,167

 
16,378

Asset retirement obligation
16,469

 
8,408

Mineral properties
10,075

 
9,878

Deferred mining costs
1,806

 
657

Construction in progress
21,619

 
56,493

 
291,205

 
198,129

Less: accumulated depreciation and depletion
42,809

 
26,367

Total property, plant and equipment, net
$
248,396

 
$
171,762


Depreciation expense was $17,117, $7,267 and $6,441 for the years ended December 31, 2018, 2017 and 2016, respectively. Depletion expense was $47, $33 and $3 for the years ended December 31, 2018, 2017 and 2016, respectively.
The Company capitalized no interest expense for the years ended December 31, 2018 and 2017, and $139 of interest expense associated with the construction of new plant and equipment for the year ended December 31, 2016.