"水晶之一种" can be translated as "a type of crystal" or "one kind of crystal" in English.
Here are a couple of example sentences to illustrate the usage:
* This is a type of crystal known for its unique clarity and color. （这是一种以其独特的清澈度和颜色而闻名的水晶。）
* One kind of crystal often used in jewelry making is quartz. （一种常用于珠宝制作的水晶是石英。）