# Relationship history for MSHA mine 1102598

Current hierarchy: **Covia Holdings LLC → Unimin Specialty Minerals Inc → Birk 2a**

- Valid-time bounds: inclusive, date granularity
- Null end: open-ended in the upstream history row; not independent proof of present control
- Transaction-time observation: 2026-10-17T05:35:58.500035+00:00

## Valid-time edges

- **operator_operates_mine:** Tammsco Inc → Birk 2a; 1950-01-01 to 1984-03-14; source msha-controller-operator-history
- **controller_controls_mine:** John  Norton → Birk 2a; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** John  Norton → Tammsco Inc; 1950-01-01 to 1984-03-14; source msha-controller-operator-history
- **operator_operates_mine:** Tammsco Inc → Birk 2a; 1984-03-15 to 1986-06-29; source msha-controller-operator-history
- **controller_controls_mine:** Avitar Industries Inc → Birk 2a; 1984-03-15 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Avitar Industries Inc → Tammsco Inc; 1984-03-15 to 1986-06-29; source msha-controller-operator-history
- **operator_operates_mine:** Unimin Specialty Minerals Inc → Birk 2a; 1986-06-30 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** S C R-Sibelco Nv et al → Birk 2a; 1986-06-30 to 2020-12-31; source msha-controller-operator-history
- **controller_controls_operator:** S C R-Sibelco Nv et al → Unimin Specialty Minerals Inc; 1986-06-30 to 2020-12-31; source msha-controller-operator-history
- **controller_controls_mine:** Covia Holdings LLC → Birk 2a; 2021-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Covia Holdings LLC → Unimin Specialty Minerals Inc; 2021-01-01 to current/open; source msha-controller-operator-history