Rety Winonazada, Listiyawati Nugraha, and S. Koesnaryo. 2020. “Limestone Hardness Classification Based on Compressive Strength Value in Ponjong District, Semanu District, and Tanjungsari District, Gunung Kidul Regency, Yogyakarta”. ReTII, October, 221-26. //journal.itny.ac.id/index.php/ReTII/article/view/2051.