# Relationship history for MSHA mine 3100375

Current hierarchy: **S C R-Sibelco Nv → Sibelco North America Inc. → Schoolhouse Quartz Plant**

- Valid-time bounds: inclusive, date granularity
- Null end: open-ended in the upstream history row; not independent proof of present control
- Transaction-time observation: 2026-10-13T11:19:05.459773+00:00

## Valid-time edges

- **controller_controls_mine:** S C R-Sibelco Nv et al → Schoolhouse Quartz Plant; 1950-01-01 to 2020-12-31; source msha-controller-operator-history
- **operator_operates_mine:** Harris Mining Company → Schoolhouse Quartz Plant; 1950-01-01 to 1986-02-28; source msha-controller-operator-history
- **controller_controls_mine:** Blue Diamond Coal Company → Schoolhouse Quartz Plant; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Blue Diamond Coal Company → Harris Mining Company; 1950-01-01 to 1986-02-28; source msha-controller-operator-history
- **operator_operates_mine:** Unimin Corporation → Schoolhouse Quartz Plant; 1986-03-01 to 2018-05-31; source msha-controller-operator-history
- **controller_controls_operator:** S C R-Sibelco Nv et al → Unimin Corporation; 1986-03-01 to 2018-05-31; source msha-controller-operator-history
- **operator_operates_mine:** Sibelco North America Inc. → Schoolhouse Quartz Plant; 2018-06-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** S C R-Sibelco Nv et al → Schoolhouse Quartz Plant; 2018-06-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** S C R-Sibelco Nv et al → Sibelco North America Inc.; 2018-06-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Covia Holdings LLC → Schoolhouse Quartz Plant; 2021-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Covia Holdings LLC → Unimin Corporation; 2021-01-01 to 2018-05-31; source msha-controller-operator-history