It is not known how rare this resemblance is，or whether it is most often seen in inclusions of silicates such as garnet，whose crystallography is generally somewhat similar to that of diamond; but when present，the resemblance is regarded as compelling evidence that the diamonds and inclusions are truly cogenetic. (4)
现在尚不知这种类似稀少到何种地步，也不知道是否它最常见于象石榴石一类的硅酸盐内含物中，而这类物质的晶体结构普遍地在某种程度上类似于金刚石的晶体结构。但一旦存在，这种类似就被视作极有说服力的证据，证明金刚石与内含物确是同源的。
难句类型：复杂修饰、插入语
解释：本句的句子既长，专有名词又多，从句层出不穷，故而难懂。在本句中出现的专有名词中，除了silicates硅酸盐这个单词常常出现于理科文章中，需要记忆之外，其他单词阅读现场简单处理一番既可：inclusions可以猜出是被包含的物质;garnet作首字母提炼叫g：crystallography只要能从词头推出这个单词与晶体有关即可。
意群训练：It is not known how rare this resemblance is，or whether it is most often seen in inclusions of silicates such as garnet，whose crystallography is generally somewhat similar to that of diamond; but when present，the resemblance is regarded as compelling evidence that the diamonds and inclusions are truly cogenetic.
