As of September 29, 2026, the three largest insider holders of MTX are Douglas T Dietrich (Chairman And Ceo, 175.97K shares), Douglas T Dietrich (Chairman And Ceo, 161.68K shares), Dj Iii Monagle (Group President, 89.07K shares).
| # | Insider | Position | Direct | Indirect | Total | Share of Insiders | Last Filed |
|---|---|---|---|---|---|---|---|
| 1 | Douglas T Dietrich | Chairman And Ceo | 337,648 | 0 | 337,648 | 45.5% | 18 May, 2026 |
| 2 | Dj Iii Monagle | Group President | 89,073 | 0 | 89,073 | 12.0% | 27 Jan, 2026 |
| 3 | Thomas J Meek | Senior Vice President | 83,852 | 0 | 83,852 | 11.3% | 05 Dec, 2022 |
| 4 | Jonathan J Hastings | Senior Vice President | 63,811 | 0 | 63,811 | 8.6% | 27 Jan, 2026 |
| 5 | Douglas W Mayger | Senior Vice President | 45,744 | 0 | 45,744 | 6.2% | 27 Jan, 2023 |
| 6 | Michael Cipolla | Vice President | 39,529 | 0 | 39,529 | 5.3% | 27 Jan, 2026 |
| 7 | Brett Argirakis | Group President | 32,600 | 0 | 32,600 | 4.4% | 27 Jan, 2026 |
| 8 | Matthew E Garth | Svp, Finance Treasury, Cfo | 27,082 | 0 | 27,082 | 3.6% | 08 Mar, 2022 |
| 9 | Erik Aldag | Svp Finance And Treasury, Cfo | 11,204 | 0 | 11,204 | 1.5% | 27 Jan, 2026 |
| 10 | Erin Cutler | Vp, Human Resources | 7,734 | 0 | 7,734 | 1.0% | 27 Jan, 2026 |
| 11 | Kristina M Johnson | Director | 1,400 | 0 | 1,400 | 0.2% | 05 May, 2025 |
| 12 | Timothy Jordan | Vice President | 1,279 | 0 | 1,279 | 0.2% | 13 May, 2026 |
| 13 | Rocky Motwani | Director | 1,192 | 0 | 1,192 | 0.2% | 17 Jun, 2025 |
Each row is that insider’s most recently reported position, from Form 4 filings over the last 60 months — which is why this total does not tie to the quarterly series above, where a quarter counts only the insiders who filed in it. Shares held through a fund or institutional portfolio are counted on the institutional ownership page instead.
| Date | Insider | Position | Transaction | Shares | Price | Value | Shares Held After | Ownership |
|---|---|---|---|---|---|---|---|---|
| 04 Sep, 2026 | Kristina M Johnson | Director | Acquired A | 10 | $0.00 | $0 | 6,008 | Direct |
| 04 Sep, 2026 | Marc E Robinson | Director | Acquired A | 45 | $0.00 | $0 | 26,960 | Direct |
| 04 Sep, 2026 | John J Carmola | Director | Acquired A | 47 | $0.00 | $0 | 28,001 | Direct |
| 04 Sep, 2026 | Robert L Clark | Director | Acquired A | 56 | $0.00 | $0 | 33,758 | Direct |
| 04 Sep, 2026 | Carolyn K Pittman | Director | Acquired A | 35 | $0.00 | $0 | 20,785 | Direct |
| 04 Sep, 2026 | Rocky Motwani | Director | Acquired A | 14 | $0.00 | $0 | 8,119 | Direct |
| 04 Sep, 2026 | Joseph C. Breunig | Director | Acquired A | 36 | $0.00 | $0 | 21,600 | Direct |
| 01 Jul, 2026 | Carolyn K Pittman | Director | Acquired A | 99 | $0.00 | $0 | 20,750 | Direct |
| 18 Jun, 2026 | Carolyn K Pittman | Director | Acquired A | 31 | $0.00 | $0 | 20,651 | Direct |
| 18 Jun, 2026 | Marc E Robinson | Director | Acquired A | 41 | $0.00 | $0 | 26,915 | Direct |
| 18 Jun, 2026 | Joseph C. Breunig | Director | Acquired A | 33 | $0.00 | $0 | 21,563 | Direct |
| 18 Jun, 2026 | Robert L Clark | Director | Acquired A | 51 | $0.00 | $0 | 33,702 | Direct |
| 18 Jun, 2026 | Kristina M Johnson | Director | Acquired A | 9 | $0.00 | $0 | 5,998 | Direct |
| 18 Jun, 2026 | Rocky Motwani | Director | Acquired A | 12 | $0.00 | $0 | 8,105 | Direct |
| 18 Jun, 2026 | John J Carmola | Director | Acquired A | 43 | $0.00 | $0 | 27,954 | Direct |
| 20 May, 2026 | Marc E Robinson | Director | Acquired A | 1,908 | $0.00 | $0 | 26,874 | Direct |
| 20 May, 2026 | John J Carmola | Director | Acquired A | 1,908 | $0.00 | $0 | 27,912 | Direct |
| 20 May, 2026 | Kristina M Johnson | Director | Acquired A | 1,908 | $0.00 | $0 | 5,989 | Direct |
| 20 May, 2026 | Robert L Clark | Director | Acquired A | 1,908 | $0.00 | $0 | 33,650 | Direct |
| 20 May, 2026 | Joseph C. Breunig | Director | Acquired A | 1,908 | $0.00 | $0 | 21,531 | Direct |