• The Journal of the Petrological Society of Korea
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• v.6 no.1
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• pp.34-44
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• 1997

The Jurassic granites, commercially called Yangu stone in the Pocheon-Euijeongbu area, have generally compact and coarse-grained textures, which could be classified into two types; grey granite(Gg) and light pink granite(Gp). Specific gravity, absorption ratio and prosity of Gg and Gp in physical property are 2.64 and 2.61, 0.32 % and 0.44 %, 0.86% and 1.13 %, respectively. These higher values of two latters of Gp than those of Gg are due to the more abundant microcracks in Gp. Compressive strength og Gg than those of Gg are due to more abundant microcracks in Gp. Compressive strength og Gg and Gp are 1,726 kg/cm2 and 1,717 kg/cm, respectively and bestrength has a positive proportion with Qz+Af+Pl(quartz+alkali feldspar+plagioclase) modes without trending with Bt+Ac(biotite+accessories). Tensile strength has the positive proportions with Qz+Af+Pl and Bt+Ac. While Bt+Ac has a negative trend with abrasive hardness, Qz+A+Pl shows a positive one. These may suggest Qz+Af+Pl mainly affects on strenghts potentional dimension stone than Gp.

• The Journal of Engineering Geology
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• v.15 no.2 s.42
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• pp.169-184
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• 2005

Unagsan and Sogrisan granites are widely distributed in the northern Gyeonggi massif and middle Ogcheon belt, respectively, and they show different petrologic characteristics as follows. The former has compact textures and light grey colors, and the latter has spotted miarolitic textures and pink colors. Most of the samples selected for tests are fresh and coarse-grained. And bored core samples were prepared so that they are vertical to the rift plane. The results of modal analysis show that Unagsan granite has significantly higher quartz and plagioclase contents (Qz+Pl) than Sogrisan granite. In contrast, alkali feldspar content (Af) of Sogrisan granite is much higher than that of Unagsan granite. Therefore, it is believed that the light grey colors of Unagsan granite are due to relatively high Qz+Pl, and the pink colors of Sogrisan granite are caused by higher Af. Fractures in Sogrisan granite have strongly perpendicular strike patterns and more dip values close to vertical compared with the fractures in Unagsan granite. Results of the fracture pattern analysis suggest that the Sogrisan granite has better potential to produce dimension stones than the Unagsan granite. However, miarolitic textures often found in the Sogrisan granite may be one of the factors reducing the granite quality. The Unagsan and Sogrisan granites have similar specific gravity values of 2.60 and 2.57, respectively. Absorption ratios and porosity values of Sogrisan granite are higher than those of Unagsan granite, and they shows linearly positive correlations. Compressive and tensile strengths of the Unagsan granite are generally higher than those of Sogrisan granite. These differences and variation trends found in physical properties of Unagsan and Sogrisan granite can be explained by the differences in the textures of Unagsan and Sogrisan granites, namely compact and miarolitic textures respectively. For Unagsan granite, compressive and tensile strengths are negatively correlated with porosity but for Sogrisan granite no specific correlations are found. This is probably due to the irregular dispersion patterns of miarolitic textures formed during the later stages of magmatic processes. Contrary to the trends found in absorption ratios, both granites have similar values of abrasive hardness, which can be explained by higher Qz+Af of the Sogrisan granite than those of the Unagsan granite and that quartz and alkali feldspar have relatively larger hardness values. For Sogrisan granite, compressive strength shows slightly positive correlations with Qz+Af+Pl and negative correlations with biotite and accessory mineral contents (Bt+Ac).

• The Journal of the Petrological Society of Korea
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• v.21 no.2
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• pp.263-275
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• 2012

Jurassic Daebo biotite granites, known as one of the main stone resources in the country, are widely and away distributed in the Pocheon and Yangju areas of the mid Gyeonggi massif. The objects of the study are mainly to reveal the unique characteristics of grain size, rock color, mineral composition, physical property and fracture system from the above biotite granites. Biotite granites from the Pocheon area (PG) and Yangju area (YG) are represented by coarse-grained and light gray, and medium to coarse-grained and grayish to light gray, respectively. In modes, main minerals of Qz+Af+Pl (quartz+alkali feldspar+plagioclase) are more increased in the PG, and accessories of biotite are more increased in the YG, which differences can cause the PG more bright light gray than the YG. Specific gravity (SG) shows somewhat more increasing in the YG than the PG. These differences can be caused by more increasing in biotite contents of higher specific gravity compared to the major minerals in the former than the latter. Absorption ratio (AR) and porosity (PR) of the PG and YG show the same values of 0.33 % and 0.86 %, respectively. In the correlations, PR vs SG and AR vs PR show gradually negative and distinctly positive trends, respectively. Compressive strength (CS) and tensile strength (TS) show increasing in the PG (CS: 1,775 $kg/cm^2$, TS: 87 $kg/cm^2$) than the YG (CS: 1,647 $kg/cm^2$, TS: 79 $kg/cm^2$). These strength characteristics could be attributed to the inherent rock textures of them. Abrasive hardness (AH) also shows a little increasing in PG, which can be caused by increase in quartz contents having higher hardness than the other major minerals. Orientations of fracture sets from the PG and YG were compared with those of vertical rift and grain planes in Mesozoic granites of the country. From the overlapped diagram, the distribution pattern between fracture sets and above vertical planes suggests that microcrack systems developed in Mesozoic granites in Korea occur also in the Daebo biotite granite bodies of the mid Gyeonggi massif. From the relation diagram showing the characteristics of fracture patterns for the above two area, PG and YG may have more potentiality for dimension and non-dimension stone resources, respectively.