There's no such thing as a "field" in XML. If you mean elements the answer is yes (duplicates are allowed). If you mean attributes then the answer is no.
<xsl:for-each select="xxx">
<xsl:value-of select="."/>
<xsl:if test="position()!=last()">/</xsl:if>
</xsl:for-each>
Or in XSLT 2.0, use the string-join function.
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference