This is the 9373rd most frequent Japanese word.
硬度
Hardness.
The word '硬度' (kōdo) is used here to describe the physical property of hardness in the context of minerals.
この鉱物の硬度を測定するには、専門的な機器が必要です。
To measure the hardness of this mineral, professional equipment is required.
The word '硬度' (kōdo) in this sentence refers to water hardness, a measure of mineral concentration in water.
水の硬度はその中に溶けているミネラルの量によって決まります。
The hardness of water is determined by the amount of minerals dissolved in it.
Here, '硬度' emphasizes the importance of material hardness in determining structural strength.